English units are the historical units of measurement used in England up to 1824, which evolved as a combination of the Anglo-Saxon and Roman systems of units. They were redefined in the United Kingdom in 1824 by a Weights and Measures Act, which retained many but not all of the unit names with slightly different values, and again in the 1970s by the International System of Units as a subset of the metric system. In modern UK usage, the term is considered ambiguous, as it could refer either to the imperial system used in the UK, or to the US customary system of unit. The common term used in the UK for the non-metric system is imperial units or imperial measurements, since they were used as a standard throughout the British Empire and the Commonwealth.

Within the United States, the same term is commonly used to refer to the United States Customary System^[1], which retains some unit names but with different values, as well as to the imperial units.

Various standards have applied to English units at different times, in different places, and for different applications.

Very little is known of the measurement units of the British Isles prior to Roman colonization in the 1st century CE. During the Roman period, Roman Britain relied on Ancient Roman units of measurement. During the Anglo-Saxon period, the North German foot of 335 millimeters (13.2 inches) was the nominal basis for other units of linear measurement. The foot was divided into 4 palms or 12 thumbs. A cubit was 2 feet, an elne 4 feet. The rod was 15 Anglo-Saxon feet, the furlong 10 rods. An acre was 4 × 40 rods, i.e., 160 square rods or 36,000 square Anglo-Saxon feet. However, Roman units continued to be used in the construction crafts. From the time of Offa King of Mercia (8th c.) until 1526 the Saxon pound, also known as the moneyers' pound (and later known as the Tower pound) was the fundamental unit of mass measurement.

Prior to the enactment of a law known as the Composition of Yards and Perches (Compositio ulnarum et perticarum)^[2] some time between 1266 and 1303, the English system of measurement had been based on that of the Anglo-Saxons, inherited from tribes from northern Germany. The Compositio retained the Anglo-Saxon rod of 5.03 metres and the acre of 4 × 40 rods. However, it redefined the yard, foot, inch, and barleycorn to 10/11 of their previous value. Thus, the rod went from 5 old yards to 5 1/2 new yards, or 15 old feet to 16 1/2 new feet. The furlong went from 600 old feet (200 old yards) to 660 new feet (220 new yards). The acre went from 36,000 old square feet to 43,560 new square feet. Scholars have speculated that the Compositio may have represented a compromise between two earlier systems of the units, the Anglo-Saxon and the Roman.

Contrary to popular belief, the Norman conquest of England had little effect on British weights and measures other than to introduce one new unit: the bushel. William the Conqueror, in one of his first legislative acts, confirmed existing Anglo-Saxon measurement, a position which was consistent with Norman policy in dealing with occupied peoples. Another popular myth is that the Magna Carta of 1215 (specifically chapter 35) had any significant effect on English weights and measures, as this document only mentions one unit (the London Quarter) but does not define it.

Later development of the English system continued by defining the units by law and issuing measurement standards. Standards were renewed in 1496, 1588 and 1758. The last Imperial Standard Yard in bronze was made in 1845; it served as the standard in the United Kingdom until the yard was internationally redefined as 0.9144 metre in 1959 (statutory implementation: Weights and Measures Act of 1963). The English system then spread to other parts of the British Empire.

Length[link]

Chart showing the relationships of distance measures.

Poppyseed 

about ¹⁄₄ of a barleycorn^[3]

Line 

¹⁄₄ of a barleycorn^[4]

Barleycorn 

Smallest Anglo-Saxon unit of length. Notionally the length of a corn of barley, its actual length was determined in relation to a particular rod of metal, typically a yard-bar, and thus 1/108th of a yard, 1/36 of foot, or 1/3 of an inch.^[5] The unit was nominally the base unit from which the inch was defined. 3 barleycorns comprising 1 inch was the legal definition of the inch in many medieval laws, both of England and Wales, from the 10th century Laws of Hywel Dda to the 1324 definition of the inch enacted by Edward II. Note the relation to the grain unit of weight. This archaic measure is still the basis for current UK and U.S. shoe sizes, with the largest shoe size taken as thirteen inches (a size 13) and then counting backwards in barleycorn units,^[6] although the original derivation was: less than 13 barleycorns: infants with no shoes; 13 to 26 barleycorns: children's sizes 1 to 12; 26 to 39 barleycorns: men's sizes 1 to 13.

Digit 

³⁄₄ inch

Finger 

⁷⁄₈ inch

Hand 

4 inches

Ynch, inch 

Anglo Saxon inch, 3 barleycorns.

Nail 

3 digits = 2 ¹⁄₄ inches = ¹⁄₁₆ yard

Palm 

3 inches

Shaftment 

Width of the hand and outstretched thumb, 6 ¹⁄₂ ynches before 1066, 6 inches thereafter

Link 

7.92 inches or one 100th of a chain.^[7]

Span 

Width of the outstretched hand, from the tip of the thumb to the tip of the little finger, 3 palms = 9 inches

Foot 

Prior to the Anglo-Saxon invasions, the Roman foot of 11.65 inches (296 mm) was used. The Anglo-Saxons introduced a North-German foot of 13.2 inches (335 mm), divided into 4 palms or 12 thumbs, while the Roman foot continued to be used in the construction crafts. In the late 13th century, the modern foot of 304.8 mm was introduced, equal to exactly 10/11 Anglo-Saxon foot.

Cubit 

From fingertips to elbow, 18 inches.

Yard 

3 feet = 36 inches.

Ell 

From fingertip of outstretched arm to opposite shoulder, 20 nails = 1 ¹⁄₄ yard or 45 inches. Mostly for measuring cloth

Fathom 

Distance fingertip to fingertip arms outstretched, 6 feet

Rod (= perch)

Used for surveying land and in architecture. The rod is the same length today as in Anglo-Saxon times. (See also perch as an area and a volume unit.)

Chain 

four linear rods. Named after the length of surveyor's chain used to measure distances until quite recently. Any of several actual chains used for land surveying and divided in links. Gunter's chain, introduced in the 17th century, is 66 feet.

Furlong 

"One plough's furrow long" (Saxon furrow is furh), nominally the distance a plough team could be driven without rest, it was actually a very precise measure of 40 rods or 600 Anglo-Saxon feet (ten percent longer than the modern foot). Thus, 660 modern feet, 40 rods or ten chains.

Mile 

Introduced after 1066, originally the Roman mile at 5000 feet, in 1592 it was extended to 5280 feet to make it an even number (8) of furlongs.

League 

Usually three miles. Intended to be an hour's walk.

Area[link]

Acre

area of land one chain (four rods) in width by one furlong in length. As the traditional furlong could vary in length from country to country, so did the acre. In England an acre was 4,840 square yards, in Scotland 6,150 square yards and in Ireland 7,840 square yards. It is a Saxon unit, meaning field. Traditionally said to be "as much area as could be ploughed in one day".

Rood

one quarter of an acre, confusingly sometimes called an acre itself in many ancient contexts. One furlong in length by one rod in width, or 40 square rods.

Carucate

an area equal to that which can be ploughed by one eight-oxen team in a single year (also called a plough or carve). Approximately 120 acres.

Bovate

the amount of land one ox can plough in a single year (also called an oxgate). Approximately 15 acres or one eighth of a carucate.

Perch

an area equal to one square rod. (See also perch as a length and volume unit.)

Virgate

the amount of land a pair of oxen can plough in a single year. Approximately 30 acres (also called yard land).

Administrative units[link]

Hide

four to eight bovates. A unit of yield, rather than area, it measured the amount of land able to support a single household for agricultural and taxation purposes.

Knight's fee

five hides. A knight's fee was expected to produce one fully equipped soldier for a knight's retinue in times of war.

Hundred or wapentake

100 hides grouped for administrative purposes.

Volume[link]

General[link]

Mouthful

about ¹⁄₂ fluid ounce (oz.)

Pony

Mouthful × 2 = 1 oz.

Jigger

1.5 oz.

Jack or Jackpot

2.5 fl. oz. (or double this for milk and beer in Northern England)

Gill

Jack × 2 = 5 fl. oz. (or double this for milk and beer in Northern England)

Cup

Gill × 2 = 10 fl. oz.

Pint

Cup × 2 = 20 fl. oz ("A pint of pure water weighs a pound and a quarter")

Quart

Pint × 2 = 40 fl. oz

Pottle or Half Gallon

Quart × 2 = 80 fl. oz or ¹⁄₂ gallon.

Gallon

Pottle × 2 = 4 Quarts = 160 fl. oz.

Peck

Gallon × 2 = 320 fl. oz.

Kenning or Pail

Peck × 2 = 4 gal.

Bushel

Kenning × 2 = 8 gal.

Strike

Bushel × 2 = 16 gal.

Coomb

Strike × 2 = 32 gal.

Cask

Coomb × 2 = 64 gal.

Barrel

Cask × 2. In the U.K. a beer barrel is 36 imperial gallons (43 US gal; 164 L). In the U.S. most fluid barrels (apart from oil) are 31.5 US gallons (26 imp gal; 119 L) (half a hogshead), but a beer barrel is 31 US gallons (26 imp gal; 117 L). An oil barrel (bbl) is 42 US gallons (34.9723 imp gal; 158.9873 L).

Hogshead

Barrel × 2. A hogshead of wine is 63 wine/63 US gallons (52.5 imp gal; 238.5 L), while a hogshead of beer or ale is 54 gallons (250 L if old beer/ale gallons, 245 L if imperial).

Butt or Pipe

Hogshead × 2 = 128 gal.

Tun

Butt × 2 = 256 gal. (A Tun would be 2,560 lb. slightly heavier than the English ton of 2240 lb.)

perch

A volume measurement of stone; one perch is equal to 16.5 ft × 1.5 ft × 1 ft = 24.75 cu. ft. of dry stone. This is derived from the more commonly known perch, a unit of length equal to 16.5 feet.^[8]

cord

128 cubic feet of firewood; a stack of firewood 4 ft × 4 ft × 8 ft.^[9]

Wine[link]

Brewery[link]

Weight[link]

Chart showing the relationships of weight measures.

The Avoirdupois, Troy and Apothecary systems of weights all shared the same finest unit, the grain, however they differ as to the number of grains there are in a dram, ounce and pound. This grain was legally defined as the weight of a grain seed from the middle of an ear of barley. There also was a smaller wheat grain, said to be ³⁄₄ (barley) grains or about 48.6 milligrams.

Avoirdupois[link]

Grain (gr) 

64.79891 mg, ¹⁄₇₀₀₀ of a pound

Dram/drachm (dr) 

27.34375 gr (sixteenth of an ounce) (possibly originated as the weight of silver in Ancient Greek coin drachma)

Ounce (oz) 

16 dr = 437.5 grains ≈ 28 g

Pound (lb) 

16 oz = 7000 grains ≈ 454 g (NB: 'lb' stands for libra)

Quarter 

¹⁄₄ cwt

Hundredweight (cwt) 

112 lb (long) or 100 lb (short)

Ton 

20 cwt

Additions:

Nail 

¹⁄₁₆ cwt = 7 lb

clove 

7 lb (wool) or 8 lb (cheese)

Stone (st) 

2 cloves = 14 lb (an Anglo-Saxon unit changed to fit in)

Tod 

2 st = ¹⁄₄ cwt (long)

Troy and Tower[link]

The Troy and Tower pounds and their subdivisions were used for coins and precious metals. The Tower pound, which is based upon an earlier Anglo-Saxon pound, was abolished in 1527.

In terms of nominal currency units, a pound was 20 shillings of 12 pennies each (i.e. 240) from the late 8th century (Charlemagne/Offa of Mercia) to 1971 in the United Kingdom.

Troy[link]

Grain (gr) 

= 64.79891 mg

Pennyweight (dwt) 

24 gr ≈ 1.56 g

Ounce (oz t) 

20 dwt = 480 gr ≈ 31.1 g

Pound (lb t) 

12 oz t = 5760 gr ≈ 373 g

Mark

8 oz t

[edit] Tower

Grain (gr) 

= ⁴⁵⁄₆₄ gr t ≈ 45.5 mg

Pennyweight (dwt) 

32 gr T = 22 ¹⁄₂ gr t ≈ 1.46 g

Tower ounce 

24 dwt T = 640 gr T = 18 ³⁄₄ dwt t = 450 gr t ≈ 29 g

Tower pound 

12 oz T = 240 dwt T = 7680 gr T = 225 dwt t = 5400 gr t ≈ 350 g

Mark

8 oz T =

Apothecary[link]

Grain (gr) 

= 64.79891 mg

Scruple (s ap) 

20 gr

Dram (dr ap) 

3 s ap = 60 gr

Ounce (oz ap) 

8 dr ap = 480 gr

Pound (lb ap) 

5760 gr = 1 lb t

Others[link]

Merchants/Mercantile pound 

15 oz tower = 6750 gr ≈ 437.4 g

London/Mercantile pound 

15 oz troy = 16 oz tower = 7200 gr ≈ 466.6 g

Mercantile stone 

12 lb L ≈ 5.6 kg

Butcher's stone 

8 lb ≈ 3.63 kg

Sack 

26 st = 364 lb ≈ 165 kg

The carat was once specified as four grains in the English-speaking world. Some local units in the English dominion were (re-)defined in simple terms of English units, such as the Indian tola of 180 grains.

See also[link]

References[link]

External links[link]

• English Customary Weights and Measures
• Jacques J. Proot's Anglo-Saxon weights & measures page. Internet Archive Wayback Machine
• Alexander Justice, "A General Discourse of the Weights and Measures" (London, 1707).