Imperial Measurement Conversion Charts and Definitions
Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2017/12/22 - Updated: 2025/05/19
Publication Type: Charts, Graphs, Tables
Category Topic: Medical Calculators and Charts - Academic Publications
Page Content: Synopsis - Introduction - Main - Insights, Updates
Synopsis: This information provides a comprehensive overview of the Imperial measurement system, detailing its origins, definitions, and the distinctions between Imperial and U.S. customary units. It features clear, well-organized charts and tables that outline conversions for length, mass, area, volume, and specialized measures such as troy and apothecaries' weights. The article explains the historical context and current usage of these units in various countries, making it especially useful for individuals navigating between measurement systems-such as seniors, people with disabilities, or anyone working with international documents, recipes, or medical instructions. The clarity and accuracy of the information are supported by the expertise of the author, a recognized advocate and editor with a strong background in accessibility and disability rights, ensuring the content is both authoritative and accessible for a diverse audience - Disabled World (DW).
Introduction
What is the Imperial System?
The 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.
Main Content
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.
| 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 (Stone Calculator) |
| 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 |
| Unit | Divisions | SI Equivalent |
|---|---|---|
| 1 minim (min) | 0.061 611 52 mL | |
| 1 fluid dram (fl dr) | 60 min | 3.696 691 mL |
| 1 fluid ounce (fl oz) | 8 fl dr | 29.573 53 mL |
| 1 gill (gi) | 4 fl oz | 118.294 1 mL |
| 1 cup (cp) or (c) | 2 gi or 8 fl oz | 236.588 2 mL |
| 1 (liquid) pint (pt) | 2 cups or 4 gi or 16 fl oz | 473.176 5 mL |
| 1 (liquid) QUART b (qt) | 2 pt or 32 fl oz | 946.352 9 mL |
| 1 (liquid) US gallon (US gal) | 4 qt or 128 fl oz or 231 cu in | 3.785 412 L |
| 1 beer barrel (bbl) | 31 gal | 117.347 8 L |
| 1 oil barrel (bbl) | 42 gal | 158.987 3 L |
| 1 hogshead | 63 gal | 238.481 0 L |
Imperial Measuring Terms
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.
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,
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)
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.
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.
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.
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.
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.
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).
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.
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
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.
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.
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.
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.
Scruple - A unit of apothecary weight. It is equivalent to a twenty-fourth part of an ounce, 1.3 grams, or 20 grains.
Troy weight - A system of units of mass customarily used for precious metals, black powder, and gemstones.
Insights, Analysis, and Developments
Editorial Note: As metrication continues to spread worldwide, resources like this remain vital for bridging the gap between traditional and modern systems of measurement. Whether for medical needs, home projects, or daily living, having reliable conversion information at hand can reduce confusion and promote independence, especially for those who may encounter barriers in accessing or interpreting technical data. This resource serves as a practical guide, bridging the gap between historical and modern measurement systems, and ensuring clarity in various applications, from healthcare to real estate - Disabled World (DW).
Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.