British-American System of Units

Discussion

introduction

In like manner there were natural measures of quantity, such as fathoms, cubits, inches, taken from the proportion of the human body, were once in use with every nation. But by a little observation, they found that one man's arm was longer or shorter than another's, and that one was not to be compared with the other, and therefore wise men who attended to these things would endeavour to fix upon some more accurate measure, that equal quantities might be of equal values. Their method became absolutely necessary when people came to deal in many commodities, and in great quantities of them.

Adam Smith—1763

What a world. What a world. This section is currently a horrible pile of notes. The intro should talk about the cultural origin of these traditional units. They evolved over longer periods and have a lot more history than the SI units. The discussion will follow this sequence: traditional units (length, mass, area, volume), non-metric scientific units (the foot-pound-second systems, and the rest). Let's start with …

length

The English system is composed of a lot of very sensible length units. Hands, feet, rods, paces — these are things I can relate to. Furlongs, fathoms, miles, yards — these make sense if you know a little bit of etymology (the study of the origins and evolution of words). Unfortunately, the conversion factors are a mess. Feet don't fit into furlongs in an easy to grasp way. There are a lot of "nice" numbers in this system — numbers like 3, 4, 5, 6, 8, 12 and 16 — but after awhile you begin to feel buried in the "special" numbers that arise from the combinatoric gyrations the system runs you through.

inch An inch is the length of three barleycorns placed end to end. The word inch comes from the Latin word for one-twelfth (uncia) since there are twelve inches in a foot. The inch is commonly subdivided into halves, quarters, eighths, sixteenths, and other powers of two; but can also be divided into hundredths (as in the caliber of firearms) or thousandths (called mils). One inch is now defined as 0.0254 m (or 2.54 cm if you prefer).
   
hand A hand is the width of a man's hand. Used to measure the height of horses and not much else. A standard hand is 4 inches.
   
foot A foot is the length of a man's foot — a convenient measuring tool for many purposes. (Convenient for men with feet, anyway.) A standard foot is 12 inches.
   
yard A yard is the length from the King's nose to his outstretched hand. Presumably, after the king held out his hand someone placed a stick in the gap and marked it. This stick would then be the standard stick of the kingdom. Yard is an Old English word for staff, rod, or stick. That makes the word yard-stick a candidate for the Department of Redundancy Department. A standard yard is 3 feet long.
   
pace The pace has its origins in Rome. The passus was measured from the heel of one foot to the heel of the same foot when it next touched the ground. This is a convenient unit for measuring walking distances (again, for men with feet). A standard pace is 5 feet long.
   
fathom The fathom is a measure of length that was commonly used by navigators. It was the length to which a man could extend his arms while measuring ropes used to determine the depth of navigable waters. The word fathom has its roots in the Old English word for embracing arms. A standard fathom is 6 feet long
   
rod A rod is a measure of length equal to 16½ feet or 5½ yards. It is also called a pole or a perch. (I'd hate to meet the budgie that needed a sixteen and a half foot perch.)
   
chain Surveyors commonly used chains for measuring distances. The most famous of these was developed by the English mathematician Edmund Gunter (1581–1626). The links of Gunter's chain were each 792/100 inches long. One hundred links gave it a total length of 792 inches, 66 feet, or 22 yards. Not a sensible number if you ask me, but then I don't play cricket. (The distance between wickets on a cricket pitch is 22 yards.)
   
furlong Literally, the length of a furrow. A sensible length for farmers that later evolved into the acre, which is discussed later in this section. A standard furrow is 220 yards long or ⅛ mile
   
mile One mile was the distance of a thousand paces: in Latin, mille passus. A pace being 5 feet gives a mile of roughly 5000 feet. The mile acquired its current value of 5280 feet (1760 yards) by the decree of the English parliament during the reign of Elizabeth I. Since this was a legal definition it became known as the statute mile — statute being another word for law.
 
From Webster's 1913 Dictionary: "The distance called a mile varies greatly in different countries. Its length in yards is …
 
  • Austria, 8,297 yards
  • Brunswick, 11,816 yards
  • England and US, 1,760 yards
  • Hungary, 9,139 yards
  • Italy, 2,025 yards
  • Netherlands, 1,094 yards
  • Norway, 12,182 yards
  • Poland, 8,100 yards
  • Prussia, 8,238 yards
  • Spain, 1,552 yards
  • Sweden, 11,660 yards
  • Switzerland, 8,548 yards
 
You can't walk on the ocean so sailors developed a variation on the thousand paces concept. A nautical mile is equal to one minute of arc measured on a great circle of the earth — basically 1/60 of 1/360 of the earth's circumference. A trip around the world would be 21,600 nautical miles if this definition worked. Unfortunately, the earth is not a perfect sphere so there is no one measurement that would qualify as its circumference. (Using the equator as the standard gives a variation on the nautical mile called the geographic mile.) The nautical mile is currently defined as 1852 m exactly, which works out to approximately …
 
1 nautical mile =  1852 m    1 inch   1 foot
1 0.0254 m 12 inches
1 nautical mile =  6076.1154855643 … feet  
 
 
This definition comes from Le Bureau International des Poids et Mesures (the International Bureau of Weights and Measures) in France — the folks responsible for maintaining Le Système International d'Unités (the International System of Units).
   
league A league is usually thought of as the distance a person could walk in an hour — 3 miles. On land, that would be 3 statute miles. At sea, 3 nautical miles. In other countries, well … I refer again to Webster's 1913 Dictionary.
A measure of length or distance, varying in different countries from about 2.4 to 4.6 English statute miles of 5280 feet each, and used (as a land measure) chiefly on the continent of Europe, and in the Spanish parts of America. The marine league of England and the United States is equal to three marine, or geographical, miles of 6080 feet each. Note: The English land league is equal to three English statute miles. The Spanish and French leagues vary in each country according to usage and the kind of measurement to which they are applied. The Dutch and German leagues contain about four geographical miles, or about 4.6 English statute miles.
   
  units     conversions
1 mil               = 0.001in
1 caliber               = 0.01in
  inch [in] = 0.0254 m (exactly)
1 hand               = 4 in
1 foot [ft]             = 12 in
1 yard [yd]         = 3 ft = 36 in
1 pace           = 5 ft = 60 in
1 fathom       = 2 yd = 6 ft = 72 in
1 rod       = 5½ yd = 16½ ft = 198 in
1 chain   = 4 rods = 22 yd = 66 ft = 792 in
1 furlong   = 10 chains = 220 yd = 660 ft = 7920 in
1 statute mile [mi] = 8 furlongs = 1760 yd = 5280 ft = 63,360 in
  nautical mile   = 1852 m (exactly) = 6076.12 ft (approximately)
1 league   = 3 miles = 5280 yd = 15,840 ft = 190,080 in
Length units of the English system

Let's move on to …

mass (or is it weight?)

Actually, it's both. The English units for mass are also units of weight for that mass in a standard gravitational field (9.80665 m/s2 exactly). This part of the English system should probably be called the French system since so many of the units have their origins in France. There were two paths: avoirdupois and troy.

These units do not seem to come in the same kind of easily relatable sizes like those for length. (There are a lot of units that just seem to mean "small" for example.) This list is also shorter than the previous one.

grain A grain was said equal to the mass of an average grain of wheat taken from the middle of an ear. There 7,000 grains in the the avoirdupois pound and 5,760 grains in the troy the pound.
   
scruple From the Latin word scrupus, a small rough pebble or a chip of stone — basically, something small. A scruple is 20 grains.
   
pennyweight At one time English pennies weighed 24 grains.
   
dram A fraction of an ounce (an eigth or a sixteenth depending on the system). The word is derived from the ancient Greek coin the drachma (δραχμή). One drachma weighed about one dram. Dram also refers informally to a serving of whiskey, especially Scotch. In this context, one might translate dram as "a wee bit".
   
ounce The word ounce has the same origin as the word inch — the Old English word for one twelfth: uncia. An inch is one-twelfth of a foot and an ounce is one twelfth of a pound. Well, sometimes. It could also be one sixteenth, but that's not the origin of the word. I think what's really going on is that in the olden days the world for twelfth was used indiscriminately for all sorts of small fractions with very little regard for mathematical consistency. I think they had other things to worry about.
   
pound Pound comes from Latin pondus for weight. The abbreviation lb for pound comes from the Roman unit libra (about three-quarters of an English pound), which comes from the Latin libro, to weigh. A variant symbol had a bar drawn through the ascenders like this ℔. In cursive form, the symbol was reduced to two vertical and two horizontal strokes like this #. This symbol for pound lives on today as the pound key on the telephone (also known as the "number sign", "hash", or "octothorpe").
   
stone A unit usually used for bulk agricultural commodities and legally defined as equal to 14 pounds. In practice, however, the weight of a stone varied with the article weighed.
   
 
  • glass: 5 lbs
  • meat, fish: 8 lbs
  • sugar, spices: 8 lbs
  • wax: 12 lbs
  • cheese: 16 lbs
  • hemp: 32 lbs
   
  The word stone is both the singular and plural form of the unit (one stone, two stone, three stone).
   
hundredweight Logically, a hundredweight should be a hundred of something — a hundred pounds would be my educated guess. This was the choice made in England way, way back and adopted by the United States at its founding. But what if you prefer the stone over the pound as your basic unit of weight? This was the case in England soon after the Americans left the Empire. The nearest multiple of a stone greater than a hundredweight is 8 stone or 112 pounds. This became the new hundredweight in England. To distinguish between the two, the original 100 pound hundredweight is called a short hundredweight or a cental while the newer 112 pound hundredweight is called a long hundredweight.
   
ton The origin of this word is the Middle English tun — a big container. Later the word also came to mean the capacity of such a container and was used as a unit of both volume and weight. The volume unit was not as popular as the weight unit except in the railroad business. The original Middle English tun was about as big as a modern boxcar. (Or was the modern boxcar about as big as a Middle English tun?) Eventually it was decided that a ton would be a good name for two thousand pounds. When the hundredweight changed in England, so too did the ton. America kept the unit at 2000 pounds while the English changed the unit to 2240 pounds. (2240 pounds is 160 stone, by the way.) As with the hundredweight, the American ton is called a short ton while the English ton is called a long ton. The similarly sized SI unit of 1000 kg is called a tonne in England or a metric ton in the United States. To misquote George Bernard Shaw, "England and America are two countries divided by a common unit system."
   
  units     conversions
1 grain [gr] = 1/7000 pound avoirdupois
1 dram [dr] = 1/256 pound avoirdupois
1 ounce [oz] = 16 drams    
1 pound [lb, ℔, #] = 16 ounces = 7000 grains
  pound avoirdupois [lb, ℔, #] = 0.45359237 kg (exactly)
1 stone [st] = 14 pounds    
1 short hundredweight [cwt] = 100 pounds    
1 long hundredweight [cwt] = 112 pounds    
1 short ton [tn] = 2000 pounds    
1 long ton [tn] = 2240 pounds    
Avoirdupois mass units of the English system
  units     conversions
1 grain [G] = 1/5760 pound troy
1 scruple [℈]     = 20 grain
1 pennyweight [dwt]     = 24 grains
1 dram [ʒ] = 3 scruples = 60 grains
1 ounce [℥] = 8 drams = 480 grains
1 pound [lb, ℔, #] = 12 ounces = 5760 grains
  pound troy   = 5760/7000 pound avoirdupois
Troy mass units of the English system

area

Generating area units should be a straightfoward affair. Take the length units and square them. This gives us very popular units like square inches, square feet, square yards, square miles and so on. We complete the list with two units from agriculture (the acre and the rood) and three quantities that relate to land surveying in the United States. These aren't really units, but I find them interesting nonetheless.

acre The word acre is related to the word agriculture. Traditionally, an acre was thought to be as much land as a pair of oxen could plow in one day. When you plow, you make a trench in the soil called a furrow. One pass across a field would leave a trench one "furrow long" — a furlong. How many furlongs could you cut in a days work? Well I have no idea, but the value that was adopted as the standard in England was the 22 yard surveyors chain developed by Edmund Gunter (1581–1626) in the Seventeenth Century. An English acre is then one furrow long by one chain wide.
  1 acre =  1 furlong  ×  1 chain  
 
  1 acre =  220 yards  ×  22 yards  =  4840 square yards
 
  1 acre =  1  mile  ×  1  mile  =  1  square mile
8 80 640
rood The word rood comes from the word rod. A rood is like an acre, only one forth as wide — as wide as a rod.
 
  1 rood =  1 furlong  ×  1 rod  =  1  acre
  4
  1 rood =  220 yards  ×  5½ yards  = 1210 square yards
 
   
subdivision Each square mile section of the Public Land Survey System was divided into four divisions or quarter-sections (½ mi × ½ mi = 160 acres) and then divided again into sixteen subdivisions or quarter-quarter-sections (¼ mi × ¼ mi = 40 acres). This last unit became a popular size for tracts of farmland and lead to the Americanisms "back forty" (the parcel of land farthest from a farmhouse) and "forty acres and a mule" (compensation that was promised to slaves after the Civil War but never delivered — a metaphor for the failure of the Reconstruction).
   
section A section is a survey tract in the United States of one square mile. It is the basic unit of the Public Land Survey System, which traces its origins back to the first decade after independence. (You may recall that George Washington was a surveyor before he was a general in the Continental Army or the president of the United States.) This system set up the rectangular coordinate system that was used to identify property boundaries in the territories outside of the original Thirteen Colonies.
   
township In the Public Land Survey System, groups of 36 sections in a contiguous 6 mile by 6 mile square are called townships. Many counties in the United States are a whole number of townships in size making their area easy to determine.
   
  units     conversions
1 square mil           = 0.000001 sq in
1 square inch [sq in] = 0.00064516 m2 (exactly)
1 square foot [sq ft]         = 144 sq in
1 square yard [sq yd]     = 9 sq ft = 1,296 sq in
1 square rod   = 30.25 sq yd = 272.25 sq ft = 39,204 sq in
1 square chain       = 16 sq rods = 484 sq yd
1 rood   = 2.5 sq chains = 40 sq rods = 1,210 sq yd
1 acre   = 10 sq chains = 160 sq rods = 4840 sq yd
1 square mile [sq mi]         = 640 acres
Area units of the English system
  units     conversions
1 subdivision           = 40 acres
1 section (1 square mile) = 16 subdivisions = 640 acres
1 township   = 36 sections = 576 subdivisions = 23,040 acres
US Public Land Survey system

volume

liquid vs. dry volume vs cubic volume

duplication of names: ounces and drams

US vs. Imperial measures

wet

minim The minim is the smallest liquid measure in the English system (as the name implies). It is equal to about one drop, in approximate terms; or 1/60 of a dram.
   
dram A fluid dram is about as much liquid as one would take in a dose of medicine (the customary use of the word) or poison (the dramatic use of the word) or spirituous liquor (the humorous use of the word — a dram is much too small to be considered a drink). It is defined as ⅛ of a fluid ounce. A fluid dram of water weighs about as much as the dram of the apothecaries weight. Thus, the conflation of the two measures in one name. Recall, that the apothecaries weight called a dram was derived from the name of a greek coin, the drachma (δραχμή).
   
teaspoon The approximate volume of a small spoon used for stirring and sipping tea. (Would it have been called the "coffeespoon" if it was invented in the US?) A standard teaspoon is ⅙ of a fluid ounce.
   
tablespoon The approximate volume of a large spoon that would commonly be used at the table. It could also have been called a soup spoon, but it wasn't. A standard tablespoon is equal to three teaspoons or ½ of a fluid ounce.
   
ounce A fluid ounce of water has a weight of about one ounce. The exact size of a fluid ounce depends on whether you use the older US gallon (128 ounces) or the newer Imperial gallon (160 ounces). More on this later.
   
gill A gill is ¼ pint. That's 4 US ounces or 5 Imperial ounces. The word is a corruption of gille, a kind of cup used to measure wine in France. Its ultimate origin was is probably a Latin word gillo meaning small pot. (A big pot in Latin became our word for gallon, by the way.) Although it's spelled the same as the organ on a fish, it's pronounced like the woman's name Jill.
   
cup Obviously, the volume of a typical cup for drinking water. A cup is 8 ounces — 8 US ounces in the US and 8 Imperial ounces in the remnants of the British Empire.
   
pint The word pint came to English from the Spanish word for a mark — pinta — probably a mark that was made on a larger measure. Exactly what that original measure was is unknown to me, but my guess is something like a gallon. In both the US and Imperial systems, a pint is ⅛ of a gallon but, as I stated before, the gallons aren't the same. The connotation of the pint as a "small" unit carries over into the word pint-size.
   
fifth A quantity of liquor equal to one fifth of a United States gallon. This is strictly an American invention and is only used when measuring hard liquor (never beer or wine).
   
quart One quarter of a gallon. A very obvious name.
   
gallon The word gallon comes from the Latin galleta and refers to a standard container about the same size as a helmet. (The Latin word for helmet is galea.) A gallon is 4 quarts or 8 pints. A US gallon of 128 US ounces of water weighs about 8 pounds by accident. An Imperial gallon of 160 Imperial ounces of water weighs very nearly 10 pounds by design. (8.34540449 pounds vs. 10.022417 pounds assuming the density of water is 1 g/cm3.) That's the whole source of contention. The English wanted a gallon that weighed something meaningful to them. Both gallons are now defined in terms of SI units: the US gallon is 3.785411784 liters and the Imperial gallon is 4.54609 liters, exactly.
   
barrel A unit barrel is about the equal to the volume of a typical wooden barrel. The size of a barrel is determined by what it contains (and also the year, but I won't get into that): 31½ US gallons of anything but petroleum, 36 Imperial gallons of beer, 26¼ Imperial gallons of wine, or 42 US gallons of peroleum
   
hogshead A container about twice the size of a barrel: 63 US gallons of anything, 52½ Imperial gallons of wine, 54 Imperial gallons of beer. The word hogshead is drived from an old Danish word for oxhead. What this has to do with anything is a mystery.

dry [still in rough note form]

pint [OE. pinte, F. pinte, fr. Sp. pinta spot, mark, pint, fr. pintar to paint; a mark for a pint prob. having been made on or in a larger measure. See {Paint}.] A measure of capacity, equal to half a quart, or four gills, — used in liquid and dry measures. See {Quart}.
   
quart [F. quarte, n. fem., fr. quart fourth. See {Quart} a quarter.] 1. A measure of capacity, both in dry and in liquid measure; the fourth part of a gallon; the eighth part of a peck; two pints.
   
peck [Perh. akin to pack; or, orig., an indefinite quantity, and fr. peck, v. (below): cf. also F. picotin a peak.] 1. The fourth part of a bushel; a dry measure of eight quarts; as, a peck of wheat. "A peck of provender." --Shak.
   
bushel [OE. buschel, boischel, OF. boissel, bussel, boistel, F. boisseau, LL. bustellus; dim. of bustia, buxida (OF. boiste), fr. pyxida, acc. of L. pyxis box, Gr. ?. Cf. {Box}.] 1. A dry measure, containing four pecks, eight gallons, or thirty-two quarts. Note: The Winchester bushel, formerly used in England, contained 2150.42 cubic inches, being the volume of a cylinder 181/2 inches in internal diameter and eight inches in depth. The standard bushel measures, prepared by the United States Government and distributed to the States, hold each 77.6274 pounds of distilled water, at 39.8[deg] Fahr. and 30 inches atmospheric pressure, being the equivalent of the Winchester bushel. The imperial bushel now in use in England is larger than the Winchester bushel, containing 2218.2 cubic inches, or 80 pounds of water at 62[deg] Fahr. 2. A vessel of the capacity of a bushel, used in measuring; a bushel measure. Is a candle brought to be put under a bushel, or under a bed, and not to be set on a candlestick? --Mark iv. 21. 3. A quantity that fills a bushel measure; as, a heap containing ten bushels of apples. Note: In the United States a large number of articles, bought and sold by the bushel, are measured by weighing, the number of pounds that make a bushel being determined by State law or by local custom. For some articles, as apples, potatoes, etc., heaped measure is required in measuring a bushel.

cubic

register ton The register ton is a unit of volume not mass, used in railroad and shipping. 1 register ton equals 100 cubic feet. (1 ton sometimes also equals 40 cubic feet!)
   
cord 1 cord of wood is eight feet wide, four feet high, and four feet deep, or 128 cubic feet; measured with a cord, thus the name
   
acre foot A good unit for reservoirs.
  units     conversions
  gallon [gal] = 4.54609 liters (exactly)
1 minim [min]                
1 dram [dr]             = 60 min
1 teaspoon [tbsp]         =   = 100 min
1 tablespoon [tbs]     = 3 tsp =   = 300 min
1 ounce [oz] = 1⅗ tbsp = 4⅘ tsp = 8 dr = 480 min
1 gill [gi]             = 5 oz
1 cup [c]             = 8 oz
1 pint [pt]         = 2½ c = 20 oz
1 quart [qt]     = 2 pt = 5 c = 40 oz
1 gallon [gal] = 4 qt = 8 pt = 20 c = 160 oz
1 peck [pk] = 8 qt = 2 gal = 8 qt = 16 pt
1 bushel [bu] = 4 pk = 8 gal = 32 qt = 64 pt
1 barrel [bbl]     = 26¼ gal (wine) = 36 gal (beer)
1 hogshead       = 52½ gal (wine) = 54 gal (beer)
1 cubic inch [cu in]                
1 cubic foot [cu ft]             = 1,728 cu in
1 cubic yard [cu yd]         = 27 cu ft = 46,656 cu in
1 register ton           = 100 cu ft    
1 acre foot   = 1,613⅓ cu yd = 43,560 cu ft    
1 cubic mile [cu mi] = 5,451,776,000 cu yd = 147,197,952,000 cu ft
Volume units of the Imperial system
  units     conversions
  gallon   = 231 cu in (exactly) = 3.785411784 liters (exactly)
1 minim [min]                
1 dram [dr]             = 60 min
1 teaspoon [tbsp]         = 1⅓ dram = 80 min
1 tablespoon [tbs]     = 3 tsp = 4 dr = 240 min
1 ounce [oz] = 2 tbsp = 6 tsp = 8 dr = 480 min
1 gill [gi]             = 4 oz
1 cup [c]             = 8 oz
1 pint [pt]         = 2 c = 16 oz
1 fifth   = ⅘ qt         = 25⅗ oz
1 quart [qt]     = 2 pt = 4 c = 32 oz
1 gallon [gal] = 4 qt = 8 pt = 16 c = 128 oz
1 barrel [bbl] = 31½ gal            
1 barrel of oil [bbl] = 42 gal            
1 hogshead   = 63 gal = 2 bbl        
Liquid volume units of the US system
  units     conversions
  bushel   = 2150.42 cu in (exactly) = 0.0316243 … (approximately)
1 pint [pt]                
1 quart [qt]             = 2 pt
1 gallon [gal]         = 4 qt = 8 pt
1 peck [pk] =   = 2 gal = 8 qt = 16 pt
1 bushel [bu] = 4 pk = 8 gal = 32 qt = 64 pt
Dry volume units of the US system

foot-pound-second

The foot-pound-second system is an attempt to make a useful scientific unit system out of the mess that is the traditional English system of units. The foot is good. (Most everybody has at least one foot.) The second is good. (Thankfully, the English units of time are the same as those used by everybody else — at least when it comes to science.) The pound, for lack of a better word, is bad. When dealing with the pound, one common question is "Do they mean mass or do they mean weight?" To be precise, one should always indicate.

Start from the pound avoirdupois, the usual unit used for mass and weight in the English system. SI dominates the world now and the English pound mass is now defined in terms of the kilogram.

pound mass = 0.45359237 kg

This value is exact by definition. It is not measured or calculated.

From here we move on to the first unit of force in the English system. You heard me right, the first. There are two — one in which the pound is a unit of weight and one in which it's a unit of mass. The pound force is defined as the weight of a pound mass in a standard gravitational field. Thus …

W  =  mg
pound force  =  (pound mass)(acceleration due to gravity)
pound force  =  (0.45359237 kg)(9.80665 m/s2)
pound force  =  4.44822162 … N

The corresponding unit of mass is the horribly named slug. The slug is the unit of mass when the pound is a unit of force. A mass of one slug will accelerate at one foot per second squared when pushed by a one pound force.

F  =  ma
1 pound force  =  (1 slug)(1 ft/s2)
(1 pound mass)(acceleration due to gravity)  =  (1 slug)(1 ft/s2)
(1 pound mass)(32.1740486 ft/s2)  =  (1 slug)(1 ft/s2)

Thus …

slug  =  32.1740486 … pound mass

In SI units, this is approximately …

slug  =  (32.1740486 … lb)(0.45359237 kg/lb)
slug  =  14.5939029 … kg

And now for the second unit of force in the English system. The poundal is the unit of force when the pound is the unit of mass. A one pound mass will accelerate at one foot per second squared when pushed by a one poundal force.

F  =  ma
poundal  =  (1 pound mass)(1 ft/s2)
poundal  =  (1 pound force)(1 ft/s2)
(acceleration due to gravity)
poundal  =  (1 pound force)(1 ft/s2)
(32.1740486 ft/s2)
 poundal  =  0.03108095 … pound force

In SI units, this is exactly …

poundal  =  (1 pound mass) (1 ft/s2)
poundal  =  (0.45359237 kg) (0.3048 m/s2)
poundal  =  0.138254954376 N

Now that we've sort of resolved the whole mass-weight debacle let's get on with this subsystem of the English system of units.

quantity full name symbol
pound force pound mass
distance foot ft
time second s
speed   ft/s
acceleration   ft/s2
acceleration due to gravity   32.1740486 ft/s2
force pound force lb (also lbf)  
poundal   pdl (lb ft/s2)
mass slug slug (lbs2/ft)  
pound mass   lb (also lbm)
energy   ft lb ft pdl
power   ft lb/s ft pdl/s
moment of inertia   slug ft2 (lb ft s2) lb ft2
torque   ft lb ft pdl
area   ft2
volume   ft3
mass density   slug/ft3 lb/ft3
weight density   lb/ft3 pdl/ft3
volume flow rate   ft3/s
mass flow rate   slug/s lb/s
weight flow rate   lb/s pdl/s
pressure   lb/ft2 pdl/ft2
dynamic viscosity   lbs/ft2 (slug/fts) pdl s/ft2 (lb/ft s)
kinematic viscosity   ft2/s
Units of the foot-pound-second systems

Base notes from the public domain Webster's Revised Unabridged Dictionary of 1913

some more units

Blah, blah, blah. So many, many units.

horsepower A unit of power, used in stating the power required to drive machinery, and in estimating the capabilities of animals or steam engines and other prime movers for doing work. It is the power required for the performance of work at the rate of 33,000 English units of work per minute; hence, it is the power that must be exerted in lifting 33,000 pounds at the rate of one foot per minute, or 550 pounds at the rate of one foot per second, or 55 pounds at the rate of ten feet per second, etc.
   
btu {Mechanical equivalent of heat} (Physics), originally defined as the number of units of work which the unit of heat can perform, equivalent to the mechanical energy which must be expended to raise the temperature of a pound of water one degree Fahrenheit; later this value was defined as one {British thermal unit} (B.t.u). Its value was found by Joule to be 772 foot pounds; later measurements give the value as 777.65 foot-pounds, equivalent to 107.5 kg-meters. This value was originally called Joule's equivalent, but the modern Joule is defined differently, being 10^{7} ergs. The B.t.u. is now given as 1,054.35 absolute Joules, and therefore 1 calorie (the amount of heat needed to raise one gram of water one degree centigrade) is equivalent to 4.186 Joules.
   
therm 100,000 btu
   
quad quadrillion btu
   
candle {Standard candle} (Photom.), a special form of candle employed as a standard in photometric measurements; usually, a candle of spermaceti so constructed as to burn at the rate of 120 grains, or 7.8 grams, per hour. {Candle power} (Photom.), illuminating power, as of a lamp, or gas flame, reckoned in terms of the light of a standard candle.
   
foot candle The amount of illumination produced by a standard candle at a distance of one foot.
   
inches of mercury
   
   
fahrenheit {Fahrenheit thermometer} is so graduated that the freezing point of water is at 32 degrees above the zero of its scale, and the boiling point at one atmosphere of pressure is 212 degrees. It is commonly used in the United States and in England.
   
  212 ℉ = 100 ℃ and 32 ℉ = 0 ℃
  T[℉] = (T[℃]*9/5 +32) or T[℃] = (T[℉] − 32)*5/9
   
rankine  
   
knot (a) A division of the log line, serving to measure the rate of the vessel's motion. Each knot on the line bears the same proportion to a mile that thirty seconds do to an hour. The number of knots which run off from the reel in half a minute, therefore, shows the number of miles the vessel sails in an hour. Hence: (b) A nautical mile, or 6080.27 feet; as, when a ship goes nautical eight miles an hour, her speed is said to be eight knots. [1913 Webster] a unit of length used in navigation; equivalent to the distance spanned by one minute of arc in latitude; 1,852 meters
   
reyn Dynamic viscosity. 144 lb s/ft2
   

Anything else? Don't answer that question.