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Grains and drams, ounces and pounds, stones and tons.
The basic unit of weight in the British system is the grain - originally
based on the
weight of a grain of barley (but note that money was based on the grain of
wheat - and that three grains of barley weigh the same as four of wheat).
This grain is the troy grain - there is no other weight of the same name.
The weight of one grain is constant throughout the many different systems of
British weights. As you will see below, the ounce and pound are anything but
contstant, but have altered to meet circumstances over a period of over a
thousand years.
The avoirdupois pound is the pound in general use today. As its name
implies, it was intended to be used for weighing heavy goods. This pound
is of 7000 grains, and is split into 16 ounces (each, therefore of 437.5
grains). Each ounce is divided into 16 drams (which my calculator makes of
27.34375 grains each - much more fun than metric isn't it?).
avoirdupois weights
| 16 drams
| = 1 ounce
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| 16 ounces
| = 1 pound
|
| 7 pounds
| = 1 clove
|
| 14 pounds
| = 1 stone
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| 28 pounds
| = 1 tod
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| 112 pounds
| = 1 hundredweight
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| 364 pounds
| = 1 sack
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| 2240 pounds
| = 1 ton
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| 2 stones
| = 1 quarter
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| 4 quarters
| = 1 hundredweight
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| 20 hundredweight
| = 1 ton
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NB: The sack is not in common use. There was a 'Butchers stone' of 8lb until
the end of 1939.
The Troy pound was of 5760 grains, and was divided into 12 ounces, so
a troy pound is lighter than an avoirdupois pound, but a troy ounce (at 480
grains) weighs more than an avoirdupois ounce. The troy pound was declared
illegal in 1878, but the troy ounce continues in use today for weighing gold.
The troy ounce is split into 480 grains, and you will see 1/2 ounce weights
marked both '240 grains' and '0.5oz'. However, the apothecaries
system also has an ounce weighing 480 grains, being divided into 8 drams
(sometimes spelled drachms) of 60 grains, each dram being split into 3
scruples, of 20 grains. To make things more fun, a 2 dram weight would be
marked '3ij' - I think that '3' means 'scruples' (there being 3 to the
dram), and the 'ij' being an old-fashioned way of quoting the Roman numeral
'ii'. It doesn't end there - there are 20 penny-weights to the troy
ounce, so the 1/2 ounce weight mentioned above could also be marked as '3iv'
or '10dwt'.
Troy & apothecaries weights
| 1 ounce
| = 480 grains
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| 1 ounce
| = 24 scruples
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| 1 ounce
| = 20 pennyweights
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| 1 ounce
| = 8 drams
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The wool pound was of 6992 grains, and was (of course) used for
weighing wool. The clove, stone and tod mentioned above were also used.
The tower pound was used for weighing coins, and was of 5400 grains.
I believe the name tower comes from Tower Hill, the site of the royal
mint. This number of grains comes from the traditional weight of an English
silver penny of 22½ grains (Troy, or grains of barley - the same as 30
grains of wheat), and 240 pennies to the pound. The tower pound was abolished
in 1527.
The London pound, or libra mercatoria (trade pound) was 7200
grains (i.e. 15 troy ounces). This died out around the middle of the 14th
century. One London stone was of 12½ London pounds.
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