2 Units of area

The units of area in the U.S. customary system are based on the square inch (sq in). Since the U.S. customary system has two differing definitions of the inch, there are also two differing definitions for the square inch. But presuming international measure is used, 1 square inch is exactly 645.16 mm².

• 1 square foot (sq ft) = 144 sq in = 929.03 cm²
• 1 square rod (sq rd) = 272.25 sq ft = 25.316 m²
• 1 acre = 10 sq ch = 1 fur * 1 ch = 160 sq rd = 43,560 sq ft = 4046.9 m²
• 1 square mile (sq mi) = 640 acres = 2.59 km²
• 1 section = 1 sq mi (survey) = 2.58999847 km²

3 Units of capacity and volume

The cubic inch, cubic foot and cubic yard are commonly used for measuring volume. In addition, there is one group of units for measuring volumes of liquids, and one for measuring volumes of dry material.

Other than the cubic foot, cubic inch and cubic yard, these units are differently sized from the units in the Imperial system, although the names of the units are similar. Also, while the U.S. has separate systems for measuring the volumes of liquids and dry material, the Imperial system has one set of units for both.

Technically speaking, since these units are defined in terms of the inch, it would make a difference whether international or survey measure was used. However, in practice, the difference between the two definitions would be imperceptible, and in any case in defining volumes international measure is used.

3.1 Volume in general

• 1 cubic inch (in³ or cu in) = 16.387064 cm³
• 1 cubic foot (ft³ or cu ft) = 1728 cu in = 28.317 L
• 1 cubic yard (yd³ or cu yd) = 27 cu ft = 7.646 hL
• 1 acre-foot = 43,560 cu ft = 325,851 gallons = 13,277.088 m³

3.2 Liquid volume

• 1 minim (min) = 61.612 µ L
• 1 fluid dram (fl dr) = 60 min = 3.697 mL
• 1 fluid ounce (fl oz) = 8 fl dr = 29.574 mL
• 1 gill (gi) = 7.21875 cu in = 4 fl oz = 118.294 mL
• 1 pint (pt) = 4 gi = 16 fl oz = 473.176 mL
• 1 fifth = 25.6 fl oz = 757.082 mL
• 1 quart (qt) = 2 pt = 32 fl oz = 946.353 mL
• 1 gallon (gal) = 231 cu in = 4 qt = 128 fl oz = 3.785411784 L

3.3 Dry volume

• 1 pint (pt) = 550.610 mL
• 1 quart (qt) = 2 pt = 1.101 L
• 1 gallon (gal) = 4 qt = 268.8 cu in = 4.405 L
• 1 peck (pk) = 8 qt = 2 gal = 8.81 L
• 1 bushel (bu) = 2150.42 cu in = 4 pk = 35.239 L

4 Units of mass

There have historically been four different English systems of mass: Tower weight, Troy weight, avoirdupois weight, and apothecaries weight. Tower weight fell out of use (due to legal prohibition) centuries ago, and was never used in the United States. Troy weight is still used to weigh precious metals. Apothecaries weight, once used in pharmacy, has been largely replaced by metric measurements. Avoirdupois weight is the primary system of mass in the U.S. customary system.

The Avoirdupois units are legally defined as measures of mass, but the names of these units are sometimes applied to measures of force. For instance, in most contexts, the pound avoirdupois is used as a unit of mass, but in the realm of physics, the term "pound" can represent " pound-force" (a unit of force properly abbreviated as " lbf").

Troy weight, avoirdupois weight and apothecaries weight are all defined in terms of the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds, for example), the relationship between the grain and these other units within each system varies. For example, in apothecaries and troy weight, the pound and ounce are the same, but are different from the pound and ounce in avoirdupois, in terms of their relationships to grains and to each other. The systems also have different units between the grain and ounce (apothecaries has scruple & dram, troy has pennyweight, and avoirdupois has just dram).

To alleviate confusion, it is typical when publishing non-avoirdupois weights to mention the name of the system along with the unit. Precious metals, for example, are often weighed in "troy ounces", because just "ounce" would be more likely to be assumed to mean an ounce avoirdupois.

The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams. All the other units of mass are defined in terms of it.

For the pound and smaller units, the U.S. customary system and the British Imperial system are identical. However, they differ when dealing with units larger than the pound. The definition of the pound avoirdupois in the British Imperial system is identical to that in the U.S. customary system.

4.1 Avoirdupois weight

See Avoirdupois

• 1 grain (gr) = 64.79891 mg
• 1 dram (dr) = 27.34375 gr = 1.772 g
• 1 ounce (oz) = 16 dr = 437.5 gr = 28.35 g
• 1 pound (lb) = 16 oz = 7000 gr = 453.59237 g
• 1 hundredweight (cwt) = 100 lb = 45.359 kg
• 1 ton (t) = 20 cwt = 2000 lb = 907.18474 kg = 0.907 t

The ton and hundredweight above are sometimes referred to as the short ton, and the short hundredweight, to distinguish them from the British Imperial ton and hundredweight, which are larger and hence are referred to as the long ton and long hundredweight. The long ton and hundredweight have limited use in the United States, although they are officially recognized as units. Any unqualified reference in the U.S. to "ton" or "hundredweight" means the short ton and hundredweight mentioned above. Sometimes the terms "net" and "gross" are used instead of "short" and "long", respectively.

• 1 long hundredweight = 112 lb = 50.802 kg
• 1 long ton = 20 long cwt = 2240 lb = 1016.047 kg = 1.016 t

4.2 Apothecaries' weight

The grain has the same definition as for avoirdupois weight.

• 1 scruple (s ap) = 20 gr = 1.296 g
• 1 dram apothecaries (dr ap) = 3 s ap = 3.888 g
• 1 ounce apothecaries (oz ap) = 1 oz t = 8 dr ap = 480 gr = 31.103 g
• 1 pound apothecaries (lb ap) = 1 lb t = 12 oz ap = 5760 gr = 373.242 g

The pound and ounce apothecaries are identical to the pound and ounce troy.

See also: Apothecaries' system of mass.

4.3 Troy weight

The grain has the same definition as for Avoirdupois weight.

• 1 pennyweight (dwt) = 24 gr = 1.555 g
• 1 ounce troy (oz t) = 20 dwt = 480 gr = 31.103 g
• 1 pound troy (lb t) = 12 oz t = 5760 gr = 373.242 g

5 Cooking measures

Measures of volume and weight used in cooking. Note that differing cooking measures are used in other countries.

• 1 teaspoon = 1/3 tbsp = 1/6 fl oz = 5 ml
• 1 tablespoon (tbsp) = 1/2 fl oz = 4 fl dr = 15 ml
• 1 cup = 8 fl oz = 240 ml

• 1 stick (of butter) = ¼ lb = 4 oz = 115 g

6 Grain measures

These are derived from the volume measures.

• 1 bushel (maize) = 56 lb = 25.401 kg
• 1 bushel (wheat) = 60 lb = 27.216 kg

7 Units of temperature

• Traditionally, degrees Fahrenheit are used in the United States to measure temperatures.
• Pure water freezes at 32 °F.
• Water saturated with common salt freezes at -6.02 °F.
• Water boils at 212 °F at 1 atmospheric pressure.
• Conversion formula:

8 Other units

• British thermal unit
• horsepower
• calorie
• degree Rankine
• board-foot
• R-value

9 See also

• SI
• Imperial units
• History of Weights and Measures
• conversion of units
• Informal conversion of common units
• metrified Imperial system

10 External link

• Source: Appendix C, NIST Handbook 44, 2002 edition.

Imperial units Systems of units US customary units

<Hide>