Tub was a unit of capacity or of weight used in Britain and elsewhere.
Contents
British unit for butter and cheese
British laws for the sale of goods defined a tub of butter as a receptacle of a size which could contain 84 pounds of butter.
Definition
1 tub of butter or cheese = 84 pounds
Conversion
1 tub = 1.5 Firkin (1 Firkin = 56 lbs)
Metric equivalent
1 tub = 38 kg
Other commodities
The Oxford English Dictionary has quotations illustrating other values of a "tub" as a unit:
In Newfoundland, Canada, a tub of coal was defined as 100 pounds, while a tub of herrings was 16 Imperial gallons and a tub of salt was 18 Imperial gallons.
References
Tub (unit) Wikipedia(Text) CC BY-SA