Imperial Measure

[doubting don]

Where did the odd 12lbs come from in one hundred weight, the abbreviation "cwt" presumably come from the roman "c" for 100 followed by "wt" for weight?
What about the ounce where the abbreviation is "oz" and not "ou" as we might expect it to be?

[Ethel]

One hundred weight (cwt) is equal to 8 stone or 4 quarts exactly.

There are 20 cwt in one ton.

Oz comes from the Italian for ounce, Onza.

[kempie]

The short hundredweight (as used in North America) is 100 lbs. This is also known as a cental to avoid confusion with...

the long hundredweight (Imperial unit), which is 112 lbs (8x14), but Britain has actually had various values of hundredweight through the ages.

Prior to the 14th Century, the stone had been set at 12� London pounds, thus giving a real 100 lb (8x12�) cwt.

The stone was later enlarged to 13 London pounds, giving a 104 lb cwt.

There was also in use for some traded commodities the 108 lb cwt.

However, in 1340 King Edward III introduced the avoirdupois system of measurement which defined the stone as 14 lbs, which brings us back to the long hundredweight.