UNITED STATES CUSTOMARY UNITS are a system of measurements commonly
used in the
The majority of U.S. customary units were redefined in terms of the
meter and the kilogram with the
CONTENTS * 1 History * 2 Units of length * 3 Units of area * 4 Units of capacity and volume * 4.1 Fluid volume
* 4.2
* 5 Units of weight * 5.1 Grain measures * 6 Cooking measures * 7 Units of temperature * 8 Other units * 9 Other names for U.S. customary units * 10 See also * 11 References * 12 External links HISTORY See also:
The
The customary system was championed by the U.S.-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century. Advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. An auxiliary of the Institute in Ohio published a poem with wording such as "down with every 'metric' scheme" and "A perfect inch, a perfect pint". One adherent of the customary system called it "a just weight and a just measure, which alone are acceptable to the Lord." The U.S. government passed the Metric Conversion Act of 1975, which
made the metric system "the preferred system of weights and measures
for U.S. trade and commerce." The legislation states that the federal
government has a responsibility to assist industry as it _voluntarily_
converts to the metric system, i.e., metrification . This is most
evident in U.S. labeling requirements on food products, where SI units
are almost always presented alongside customary units. According to
the
U.S. customary units are widely used on consumer products and in industrial manufacturing. Metric units are standard in science, medicine, as well as many sectors of industry and government, including the military . There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction than a measurement in millimeters, or that foot-inch measurements are more suitable when distances are frequently divided into halves, thirds and quarters, often in parallel. The metric system also lacks a parallel to the foot. Other nations had, or still have unofficially, customary units of their own, sometimes very similar in name and measure to U.S. customary units, since they often share the same Germanic or Roman origins. Frequently, however, these units designate quite different sizes. For example, the mile ranged by country from one-half to five U.S. miles; foot and pound also had varying definitions. Historically, a wide range of non-SI units were used in the U.S. and in Britain, but many have fallen into disuse. This article deals only with the units commonly used or officially defined in the U.S. UNITS OF LENGTH UNIT DIVISIONS SI EQUIVALENT Exact relationships shown in BOLDFACE INTERNATIONAL 1 _point_ (p) 352.777778 µm 1 _pica_ (P̸) 12 P 4.233333 mm 1 _inch _ (in or ") 6 P̸ 25.4 MM 1 _foot _ (ft or ') 12 IN 0.3048 M 1 _yard _ (yd) 3 FT 0.9144 M 1 _mile _ (mi) 5280 FT or 1760 YD 1.609344 KM US SURVEY 1 link (li) 33⁄50 FT or 7.92 in 0.201168 m 1 (survey) foot (ft) 1200⁄3937 M 0.30480061 m 1 rod (rd) 25 LI or 16.5 FT 5.02921 m 1 chain (ch) 4 RD or 66 FT 20.11684 m 1 furlong (fur) 10 CH 201.1684 m 1 survey (or statute) mile (mi) 8 FUR 1.609347 km 1 league (lea) 3 MI 4.828042 km INTERNATIONAL NAUTICAL 1 fathom (ftm) 2 YD 1.8288 M 1 cable (cb) 120 FTM or 1.091 fur 219.456 M 1 nautical mile (NM or nmi) 8.439 cb or 1.151 mi 1.852 KM For measuring length, the U.S. customary system uses the inch , foot
, yard , and mile , which are the only four customary length
measurements in everyday use. Since July 1, 1959, these have been
defined on the basis of 1 yard = 0.9144 meters except for some
applications in surveying. The U.S., the
When international measure was introduced in the English-speaking countries, the basic geodetic datum in North America was the North American Datum of 1927 (NAD27), which had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893, that is 1 foot = 1200⁄3937 meters: this definition was retained for data derived from NAD27, but renamed the _US survey foot_ to distinguish it from the international foot. For most applications, the difference between the two definitions is insignificant – one international foot is exactly 0.999998 of a US survey foot, for a difference of about 1⁄8 inch (3 mm) per mile – but it affects the definition of the State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles. The NAD27 was replaced in the 1980s by the
State legislation is also important for determining the conversion factor to be used for everyday land surveying and real estate transactions, although the difference (2 ppm ) is of no practical significance given the precision of normal surveying measurements over short distances (usually much less than a mile). Twenty-four states have legislated that surveying measures should be based on the US survey foot, eight have legislated that they be made on the basis of the international foot, and eighteen have not specified the conversion factor from metric units. UNITS OF AREA UNIT DIVISIONS SI EQUIVALENT Exact relationships shown in BOLDFACE 1 square survey foot (sq ft or ft2) 144 square inches 0.09290341 m2 1 square chain (sq ch or ch2) 4356 SQ FT (SURVEY) or 16 SQ RODS 404.6873 m2 1 acre 43560 SQ FT (SURVEY) or 10 SQ CH 4046.873 m2 1 section 640 ACRES or 1 SQ MILE (SURVEY) 2.589998 km2 1 survey township (twp) 36 SECTIONS or 4 SQ LEAGUES 93.23993 km2 The most widely used area unit with a name unrelated to any length unit is the acre . The National Institute of Standards and Technology contends that customary area units are defined in terms of the square survey foot, not the square international foot. Conversion factors are based on Astin (July 27, 1968) and National Institute of Standards and Technology (2008). UNITS OF CAPACITY AND VOLUME VOLUME IN GENERAL UNIT DIVISIONS SI EQUIVALENT 1 cubic inch (cu in) or (in3) 16.387064 ML 1 cubic foot (cu ft) or (ft3) 1728 CU IN 28.31685 L 1 cubic yard (cu yd) or (yd3) 27 CU FT 764.554857984 L 0.764554857984 m3 1 acre-foot (acre ft) 43560 CU FT 1613.333 cu yd 1.233482 ML 1233.482 m3 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 inch, cubic foot 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. FLUID VOLUME LIQUID VOLUME Most common measures shown in _italic_ font Exact conversions in BOLD font UNIT DIVISIONS SI EQUIVALENT 1 minim (min) ~1 drop or 0.95 grain of water 61.611519921875 μL 1 US fluid dram (fl dr) 60 MIN 3.6966911953125 ML 1 _teaspoon _ (tsp) 80 MIN 4.92892159375 ML 1 _tablespoon _ (Tbsp) 3 TSP or 4 FL DR 14.78676478125 ML 1 _US fluid ounce _ (fl oz) 2 TBSP or 1.0408 oz av of water 29.5735295625 ML 1 US shot (jig) 1.5 FL OZ or 3 TBSP 44.36029434375 ML 1 US gill (gi) 2 2⁄3 JIG or 4 FL OZ 118.29411825 ML 1 _US cup _ (cp) 2 GI or 8 FL OZ 236.5882365 ML 1 (liquid) _US pint _ (pt) 2 CP or 16.65 oz av of water 473.176473 ML 1 (liquid) _US quart _ (qt) 2 PT 0.946352946 L 1 (liquid) _US gallon _ (gal) 4 QT or 231 CU IN 3.785411784 L 1 (liquid) barrel (bbl) 31.5 GAL or 1⁄2 HOGSHEAD 119.240471196 L 1 oil barrel (bbl) 1 1⁄3 (LIQUID) BARREL or 42 GAL or 2⁄3 HOGSHEAD 158.987294928 L 1 hogshead 1.5 OIL BARRELS or 63 GAL or 8.421875 CU FT or 524.7 lb of water 238.480942392 L One US fluid ounce is 1⁄16 of a US pint, 1⁄32 of a US quart, and 1⁄128 of a US gallon. The teaspoon, tablespoon, and cup are defined in terms of a fluid ounce as 1⁄6, 1⁄2, and 8 fluid ounces. The fluid ounce derives its name originally from being the volume of one ounce avoirdupois of water, but in the US it is defined as 1⁄128 of a US gallon. Consequently, a fluid ounce of water weighs about 1.041 ounces avoirdupois. The saying "a pint's a pound the world around" refers to 16 US fluid ounces of water weighing approximately (about 4% more than) one pound avoirdupois. An imperial pint of water weighs a pound and a quarter (20 oz). A 23.7 US fl oz (700 mL) bottle displaying both US and metric units. There are varying standards for barrel for some specific commodities, including 31 gal for beer, 40 gal for whiskey or kerosene, and 42 gal for petroleum. The general standard for liquids is 31.5 gal or half a hogshead. The common 55 gallon size of drum for storing and transporting various products and wastes is sometimes confused with a barrel, though it is not a standard measure. In the U.S., single servings of beverages are usually measured in fluid ounces. Milk is usually sold in half pints (8 fluid ounces), pints, quarts, half gallons, and gallons. Water volume for sinks, bathtubs, ponds, swimming pools, etc., is usually stated in gallons or cubic feet. Quantities of gases are usually given in cubic feet (at one atmosphere). Minims, drams and gill are rarely used currently. The gill is often referred to as a "half-cup". DRY VOLUME DRY VOLUME UNIT DIVISIONS SI EQUIVALENT 1 (dry) pint (pt) 33.60 cu in 0.5506105 L 1 (dry) quart (qt) 2 PT 1.101221 L 1 (dry) gallon (gal) 4 QT or 268.8025 CU IN 4.404884 L 1 peck (pk) 2 GAL 8.809768 L 1 bushel (bu) 4 PK or 1.244 cu ft 35.23907 L 1 (dry) barrel (bbl) 7056 CU IN or 3.281 bu 115.6271 L
UNITS OF WEIGHT Main articles:
Conversions TYPE UNIT DIVISIONS SI EQUIVALENT AVOIRDUPOIS 1 grain (gr) 1⁄7000 LB 64.79891 MG 1 dram (dr) 27 11⁄32 GR or 8.859 carats 1.7718451953125 G _1 ounce _ (oz) 16 DR 28.349523125 G _1 pound _ (lb) 16 OZ 453.59237 G 1 US hundredweight (cwt) 100 LB 45.359237 KG 1 long hundredweight 112 LB 50.80234544 KG _1 ton _ (short ton) 20 US CWT or 2000 LB 907.18474 KG 1 long ton 20 LONG CWT or 2240 LB 1016.0469088 KG TROY 1 grain (gr) 1⁄7000 LB or 1⁄5760 LB T 64.79891 MG 1 pennyweight (dwt) 24 GR or 7.776 carats 1.55517384 G 1 troy ounce (oz t) 20 DWT 31.1034768 G 1 troy pound (lb t) 12 OZ T or 13.17 oz 373.2417216 G Most common measures shown in _italics_ Exact conversions shown in BOLD There have historically been five different English systems of mass:
tower , apothecaries\' , troy , avoirdupois , and metric . Of these,
the avoirdupois weight is the most common system used in the U.S.,
although
The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams by agreement between the U.S., the United Kingdom, and other English-speaking countries in 1959. Other units of mass are defined in terms of it. The avoirdupois pound is legally defined as a measure of mass , but the name pound is also applied to measures of force . For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force ". The slug is another unit of mass derived from pound-force. Troy weight, avoirdupois weight, and apothecaries' weight are all built from 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), the relationship between the grain and these other units within each system varies. For example, in apothecary 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 and dram , troy has pennyweight , and avoirdupois has just dram, sometimes spelled _drachm_). The dram in avoirdupois weighs just under half of the dram in apothecaries'. The fluid dram unit of volume is based on the weight of 1 dram of water in the apothecaries' system. 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. 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 imperial system is identical to that in the U.S. customary system. In the U.S., only the ounce, pound and short ton – known in the country simply as the ton – are commonly used, though the hundredweight is still used in agriculture and shipping. The grain is used to describe the mass of propellant and projectiles in small arms ammunition . It was also used to measure medicine and other very small masses. GRAIN MEASURES In agricultural practice, a bushel is a fixed volume of 2150.42 cubic inches. The mass of grain will therefore vary according to density. Some nominal weight examples are:- * 1 bushel (corn) = 56 lb = 25.4012 kg * 1 bushel (wheat) = 60 lb = 27.2155 kg * 1 bushel (barley) = 48 lb = 21.7724 kg In trade terms a bushel is a term used to refer to these nominal
weights, although even this varies. With oats,
COOKING MEASURES Main article:
Common volume measures in English-speaking countries (Comparable measures listed for comparison purposes.) MEASURE AUSTRALIA CANADA UK US US FDA
Cup 250 mL 250 mL 284.13 mL 236.59 mL 240 mL
The most common practical cooking measures for both liquid and dry ingredients in the U.S. (and many other countries) are the teaspoon, tablespoon, and cup, along with halves, thirds, quarters, and eighths of these. Pounds, ounces, fluid ounces, and common sizes are also used, such as can (presumed size varies depending on product), jar, square (e.g., 1 oz of chocolate), stick (e.g., 4 oz butter), or fruit/vegetable (e.g., a half lemon, two medium onions). UNITS OF TEMPERATURE Degrees
The relationship between the different temperature scales is linear but the scales have different zero points, so conversion is not simply multiplication by a factor: pure water is defined to freeze at 32 °F = 0 °C and boil at 212 °F = 100 °C at 1 atm ; the conversion formula is easily shown to be: = 9 5 + 32 {displaystyle ={frac {9}{5}}+32} or inversely as = 5 9 ( 32 ) {displaystyle ={frac {5}{9}}(-32)} . OTHER UNITS * 1 board-foot = 1 ft × 1 ft × 1 in = 2.360 dm 3
* 1
Sizing systems are used for various items in commerce, several of which are U.S.-specific: *
OTHER NAMES FOR U.S. CUSTOMARY UNITS The
Other common ways of referring to the system in the U.S. are: "Standard", "Customary", or, erroneously: "Imperial", or "English" (which refers to the pre-1824 reform measures used throughout the British Empire). Another term is the foot–pound–second (FPS) system, as opposed to centimeter–gram–second (CGS) and meter–kilogram–second (MKS) systems. Tools and fasteners with sizes measured in inches are sometimes called "SAE bolts" or "SAE wrenches" to differentiate them from their metric counterparts. The Society of Automotive Engineers originally developed fasteners standards using U.S. units for the U.S. auto industry; the organization now uses metric units. SEE ALSO *
REFERENCES * ^ T.C. Mendenhall , Superintendent of Standard Weights and
Measures. Order of April 5, 1893 Archived September 30, 2012, at the
EXTERNAL LINKS * Rowlett's A Dictionary of Units of Measurement * v * t * e CURRENT GENERAL * |

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