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Pound (British Merchants' system)

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Wikipedia.png This page uses content from the English Wikipedia. The original article was at Pound (mass)#Merchants' pound. The list of authors can be seen in the page history. As with the Units of Measurement Wiki, the text of Wikipedia is available under Creative Commons License see Wikia:Licensing.


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 merchants' pound (mercantile pound, libra mercantoria or commercial pound) was equal to 9,600 wheat grains (15 tower ounces or 6,750 grains) and was used in England until the 14th century for most goods (other than money, spices and electuaries).[1]

Relationship between merchants' and tower weightsEdit

1 mercantile pound (15 oz) = 9,600 tower grains = 6,750 troy grains
1 tower pound (12 oz) = 7,680 tower grains = 5,400 troy grains
1 tower ounce (20 dwt) = 640 tower grains = 450 troy grains
1 tower pennyweight (dwt) = 32 tower grains = 22½ troy grains

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. Zupko, Ronald Edward (1985-12-01). Dictionary of Weights and Measures for the British Isles: The Middle Ages to the 20th Century. DIANE Publishing. ISBN 087169168X. 

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