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This page describes an obsolete unit.

The unit described on this page was in use prior to modern methods of precision measurement. It was based on a standard which is no longer available, and which is not capable of being calibrated against modern measurement units. Therefore, the equivalence to modern SI units or to current United States customary units can only be considered approximate.



The tower grain was the finest unit of the British tower system of mass/weight, intended to represent the weight of a grain of wheat. It had the value of 45/64 of a troy grain (0.703125 troy grain) by definition, or 1/7680 of a tower pound. (Thus, reversing the definition, 1.42222222 tower grains = 64/45 tower grains = 1 troy grain.)

HistoryEdit

The history of the grain can be traced back to a royal decree in 13th century England:

By consent of the whole Realm the King's Measure was made, so that an English Penny, which is called the Sterling, round without clipping, shall weigh Thirty-two Grains of Wheat dry in the midst of the Ear; Twenty-pence make an Ounce; and Twelve Ounces make a Pound. — Henry III of England[1]

This text has been taken to refer to the troy pound, so that the reference to sterling pennies is purely symbolic. More correctly, however, the pound in question is the Tower pound, and it talks about the actual mass of real sterling pennies. The Tower pound, abolished in 1527, consisted of 12 ounces like the troy pound, but was 1/16 lighter.

Comparison of different English pounds

English pounds
Unit Pounds Ounces Grains Metric
metric Lond. avdp. merc. troy tower troy tower avdp. troy tower g kg
Metric 1 15/14 11/10 8/7 4/3 10/7 ≈ 16 ≈ 171/7 ≈ 173/5 ≈ 7716 ≈ 10974 500 1/2
London 14/15 1 36/35 16/15 5/4 4/3 15 16 1616/35 7200 10240 ≈ 467 7/15
Avoirdupois 10/11 35/36 1 28/27 175/144 35/27 147/12 155/9 16 7000 99555/9 ≈ 454 9/20
Merchant 7/8 15/16 27/28 1 75/64 5/4 141/16 15 153/7 6750 9600 ≈ 437 7/16
Troy 3/4 4/5 144/175 64/75 1 16/15 12 124/5 1329/175 5760 8192 ≈ 373 3/8
Tower 7/10 3/4 27/35 4/5 15/16 1 111/4 12 1212/35 5400 7680 ≈ 350 7/20


ReferencesEdit

  1. Connor, R.D.; Simpson, A.D.C. (c2004). Weights and Measures in Scotland. East Linton. 

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