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Imperial Measurements

What is the Imperial System?

Imperial units or the Imperial system is a collection of units, first defined in the British Weights and Measures Act of 1824.

Imperial units are not used in the United States. However the U.S. system of units is similar to the Imperial system which was used officially in the United Kingdom until 1995. The customary units in use there are historically derived from units which were in use in England at the time of settlement. The measurements of most of these units in England itself were subsequently changed.

The distinction between the imperial system and the U.S. customary units (also called standard or English units) or older British/English units/systems and newer additions is often not drawn precisely. Most length units are shared between the imperial and U.S. systems, albeit partially and temporally defined differently.

In the 1970s the metric system and SI units were introduced in Canada to replace the imperial system. Within the government, efforts to implement the metric system were extensive; almost any agency, institution, or function provided by the government uses SI units exclusively. Imperial units were eliminated from all road signs.

Some imperial measurements remain in limited use in Australia, India, Malaysia and New Zealand. Real estate agents continue to use acres and square feet to describe area in conjunction with hectares and square metres.

Imperial and US Measuring System
Length Measurements
12 inches = 1 foot
3 feet = 1 yard
220 yards = 1 furlong
8 furlongs = 1 mile
5280 feet = 1 mile
1760 yards = 1 mile
Mass and Weights
437.5 grains = 1 ounce
16 ounces = 1 pound
14 pounds = 1 stone
100 pounds = 1 hundredweight
20 cwt = 1 ton
2000 pounds = 1 short ton
2240 pounds = 1 long ton
Liquid Capacity
16 fluid ounces = 1 pint
4 gills = 1 pint
2 pints = 1 quart
4 quarts = 1 gallon
8 pints = 1 gallon
Area Measurements
144 sq. inches = 1 square foot
9 sq. feet = 1 square yard
43,560 sq. ft = 1 acre
4840 sq. yards = 1 acre
640 acres = 1 square mile
Troy Weights
24 grains = 1 pennyweight
20 pennyweights = 1 ounce
12 ounces = 1 pound
Apothecaries' Measures
60 minims = 1 fl.dram
8 fl.drams = 1 fl. ounce
16 fl. ounces = 1 pint
Volume Measurement
1728 cu. inches = 1 cubic foot
27 cu. feet = 1 cubic yard
Apothecaries Weights
20 grains = 1 scruple
3 scruples = 1 dram
8 drams = 1 ounce
12 ounces = 1 pound
Dry Capacity
16 fluid ounces = 1 pint
2 pints = 1 quart
8 quarts = 1 peck
4 pecks = 1 bushel

U.S Liquid Volume Measurements
UnitDivisionsSI Equivalent
1 minim (min)0.061 611 52 mL
1 fluid dram (fl dr)60 min3.696 691 mL
1 fluid ounce (fl oz)8 fl dr29.573 53 mL
1 gill (gi)4 fl oz118.294 1 mL
1 cup (cp) or (c)2 gi or 8 fl oz236.588 2 mL
1 (liquid) pint (pt)2 cups or 4 gi or 16 fl oz473.176 5 mL
1 (liquid) QUART b (qt)2 pt or 32 fl oz946.352 9 mL
1 (liquid) US gallon (US gal)4 qt or 128 fl oz or 231 cu in3.785 412 L
1 beer barrel (bbl)31 gal117.347 8 L
1 oil barrel (bbl)42 gal158.987 3 L
1 hogshead63 gal238.481 0 L

Imperial Measuring Terms:

Avoirdupois - The avoirdupois system is a system of weights (or, properly, mass) based on a pound of sixteen ounces. It is the everyday system of weight used in the United States. It is still widely used by many people in Canada and the United Kingdom despite the official adoption of the metric system,

Troy weight - A system of units of mass customarily used for precious metals, black powder, and gemstones.

Peck - A peck is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 8 dry quarts, or 16 dry pints. Two pecks make a kenning (obsolete), and four pecks make a bushel.

Bushel - A bushel is a unit of dry volume, usually subdivided into eight local gallons in the systems of Imperial units and U.S. customary units. It is used for volumes of dry commodities, not liquids, most often in agriculture.

Dram - The dram was historically both a coin and a weight. Currently it is both a small mass in the Apothecaries' system of weights and a small unit of volume. The Greek drachm is a weight of 1⁄100 Greek mine, which is about 4.37 grams. The Roman drachm is a weight of 1⁄96 Roman pounds, which is about 3.41 grams.

Pennyweight - A pennyweight (dwt) is a unit of mass which is the same as 24 grains, 1/240th of a troy pound, 1/20th of a troy ounce, approximately 0.055 ounces or approximately 1.555 grams.

Grain - A grain is a unit of measurement of mass that is based upon the mass of a single seed of a typical cereal. Since 1958, the grain or troy grain measure has been internationally defined with the metric system equation: 1.0gr = 64.79891mg - i.e. 1 grain is exactly 64.79891 milligrams. The grain is the only unit of mass measure common to the traditional three English mass and weight systems (avoirdupois, Apothecaries', troy). Moreover, the measure for pearls and diamonds, the pearl grain and the metric grain, are equal to quarter of a (metric) carat, i.e. 50mg (0.77gr).

Scruple - A unit of apothecary weight. It is equivalent to a twenty-fourth part of an ounce, 1.3 grams, or 20 grains.

Minim- The minim is a unit of volume in both the imperial and US customary systems of measurement. Specifically it is 1/60 of a fluidram or 1/480 of a fluid ounce.

Gill - The gill is a unit of measurement for volume equal to a quarter of a pint. It is no longer in common use, except in regard to the volume of alcoholic spirits measures.

Rod - The rod is a unit of length equal to 5.5 yards, 11 cubits, 5.0292 meters, 16.5 feet, or 1/320 of a statute mile. A rod is the same length as a perch and a pole.

Chain - A chain is a unit of length; it measures 66 feet or 22 yards (20.1168m). There are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains.

Hundred weight -A unit of measurement for mass in U.S. customary units and was historically used in the Imperial system in the United Kingdom and the British Commonwealth. However, its definition differs in the two systems. In Imperial units, a hundredweight ('long') is defined as 112 pounds avoirdupois, or 8 stone, or four quarters (50.80234544 kg). In U.S. customary units, a hundredweight ('short') is defined as 100 pounds (equivalent to 45.359237 kg). The short hundredweight is also the normal hundredweight in Canada. The short hundredweight is also called a cental.

Furlong - A furlong is a measure of distance in imperial units and U.S. customary units. It is equal to one-eighth of a mile or 660 feet or 201.168 metres.

Acre - The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. One acre comprises 4,840 square yards or 43,560 square feet.

Link - The link is a unit of length in the imperial system. The unit was based on Gunter's measurement where a metal chain consisting of 100 links was in surveying property. In the English-speaking world prior to the 20th century, links were commonly used for this function but are rarely used now. 1 link = 0.01 chain = 7.92 inches = 201.168 millimeters

BTU - The British thermal unit is a unit of energy used in the power, steam generation, heating and air conditioning industries. In North America, the term BTU is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills, and air conditioners.

One BTU is approximately:

1 054 - 1 060 J (joules)
2.931 by 10-4 kWh (kilowatt hours)
252 - 253 cal (calories, or "little calories")
0.25 kcal (kilocalories, "large calories", or "food calories")
25 031 - 25 160 ft-pdl (foot-poundal)
778 - 782 ft-lbf (foot-pounds-force).

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