The imperial system of units, imperial system or imperial units (also known as British Imperial or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments. The imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825.
The system came into official use across the British Empire in 1826. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, but imperial units are still used in the United Kingdom and some other countries formerly part of the British Empire.
A thousandth of an inch is a derived unit of length in a system of units using inches. Equal to 1⁄1000 of an inch, a thousandth is commonly called a thou /ˈθaʊ/ (used for both singular and plural) or particularly in North America a mil (plural mils).
The thou, or mil, is most commonly used in engineering and manufacturing in non-metric countries. For example, in specifying:
The thickness of items such as paper, film, foil, wires, paint coatings, latex gloves, plastic sheeting, and fibers.
For example, most plastic ID cards are about 30 thou (0.76 mm) in thickness.
Card stock thickness in the United States, where mils are also called points.
Gauge (diameter) of strings in stringed instruments.
The barleycorn is a former English unit of length equal to 1⁄3 of an inch (i.e. about 8.47 mm). It is still used as the basis of shoe sizes in English-speaking countries.
Inch is equal to 1⁄36 yard or 1⁄12 of a foot. Derived from the Roman uncia (“twelfth”), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb. Inches are commonly used to specify the diameter of vehicle wheel rims, and the corresponding inner diameter of tyres – the last number in a Car/Truck tire size such as 235/75 R16; the first two numbers give the width (normally expressed in millimetres for cars and light trucks) and aspect ratio of the tyre (height 75% of width in this example), the R Designates a Radial Ply Construction.
Since the International Yard and Pound Agreement of 1959, one foot is defined as 0.3048 meters exactly. In customary and imperial units, one foot comprises 12 inches and one yard comprises three feet.
Historically the “foot” was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems. It varied in length from country to country, from city to city, and sometimes from trade to trade. Its length was usually between 250 mm and 335 mm and was generally, but not always, subdivided into 12 inches or 16 digits.
Since 1959 it is by international agreement standardized as exactly 0.9144 meters. 1,760 yards is equal to 1 mile. The name derives from the Old English gerd, gyrd etc. which was used for branches, staves, and measuring rods. It is first attested in the late-7th century laws of Ine of Wessex, where the “yard of land” mentione is the yardland, an old English unit of tax assessment equal to 1⁄4 hide.
The yard is the distance from the tip of the nose to the end of the middle finger of the outstretched hand.
The chain is a unit of length equal to 66 feet (22 yards). It is subdivided into 100 links or 4 rods. There are 10 chains in a furlong, and 80 chains in one statute mile. In metric terms, it is 20.1168 m long.
A furlong is a measure of distance in imperial units and U.S. customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 metres.
The mile, sometimes the international mile to distinguish it from other miles, is the British imperial unit and the US customary unit, both systems are based on the older English unit of length equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.
The chain is a unit of length equal to 66 feet (22 yards). It is subdivided into 100 links or 4 rods. There are 10 chains in a furlong, and 80 chains in one statute mile. In metric terms, it is 20.1168 m long.
A furlong is a measure of distance in imperial units and U.S. customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 metres.
The mile, sometimes the international mile to distinguish it from other miles, is the British imperial unit and the US customary unit, both systems are based on the older English unit of length equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.
The mile is a Roman unit, originally defined to be the length of 2000 steps of a Roman legion.
A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume (also called capacity) typically used for measuring liquids. Various definitions have been used throughout history, but only two are still in common use: the British Imperial and the United States customary fluid ounce.
An imperial fluid ounce is 1⁄20 of an imperial pint, 1⁄160 of an imperial gallon or approximately 28.41 ml.
A US fluid ounce is 1⁄16 of a US fluid pint and 1⁄128 of a US liquid gallon or approximately 29.57 ml, making it about 4.08% larger than the imperial fluid ounce.
The gallon is a unit of measurement for volume and fluid capacity in both the US customary units and the British imperial systems of measurement. Three significantly different sizes are in current use:
the imperial gallon (imp gal), defined as 4.54609 litres, which is or was once used in the United Kingdom, Canada, and some Caribbean nations;
the US gallon (US gal) defined as 231 cubic inches (exactly 3.785411784 litres), which is used in the US and some Latin American and Caribbean countries; and
the US dry gallon (“usdrygal”), defined as 1⁄8 US bushel (exactly 4.40488377086 litres).
In the 19th and 20th centuries, the UK used three different systems for mass and weight.
•troy weight, used for precious metals;
•avoirdupois weight, used for most other purposes; and
•apothecaries’ weight, now virtually unused since the metric system is used for all scientific purposes.
The word avoirdupois is from Anglo-Norman French aveir de peis (later avoir du pois), literally “goods of weight” (Old French aveir, as verb meaning “to have” and as noun meaning “property, goods”, comes from the Latin habere, “to have, to hold, to possess something”; de = “from”/”of”, cf. Latin; peis = “weight”, from Latin pensum). This term originally referred to a class of merchandise: aveir de peis, “goods of weight”, things that were sold in bulk and were weighed on large steelyards or balances.
A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and Apothecaries’ system, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single ideal seed of a cereal. From the Bronze Age into the Renaissance the average masses of wheat and barley grains were part of the legal definitions of units of mass.
The Attic Greek drachma was a weight of 6 obols, 1⁄100 Greek mina, or about 4.37 grams. The Roman drachma was a weight of 1⁄96 Roman pounds, or about 3.41 grams. A coin weighing one drachma is known as a stater, drachm, or drachma. The Ottoman dirhem was based on the Sassanian drachm, which was itself based on the Roman dram/drachm. In the avoirdupois system, the dram is the mass of 1⁄256 pound or 1⁄16 ounce. The dram weighs exactly 1.7718451953125 grams. Dram is used informally to mean a small amount of spirituous liquor, especially Scotch whisky. The unit is referenced by the phrase dram shop, the US legal term for an establishment that serves alcoholic beverages.
Besides the common ounce, several other ounces are in current use:
The troy ounce of 31.1034768 grams is used for the mass of precious metals such as gold, silver, platinum, palladium, rhodium, etc.
The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces.
The libra (Latin for “scales / balance”) is an ancient Roman unit of mass that was equivalent to approximately 328.9 grams. It was divided into 12 unciae (singular: uncia), or ounces. The libra is the origin of the abbreviation for pound, “lb”.
For more imperial ve metric system comparisons and definitions of units, you can download the presentation below:
For all kinds of conversions, please visit:
The Lectures 