Mass conversion

The unit of mass is the kilogram. The kilogram is one of the seen base units of the SI-unit system. All other units are derived from the base units.
In the 18th century the kg was defined by a mass of a cubic decimeter water.  Since 1898 kg equals to the mass of the international protortype. It is made of platinum-iridium and stores in Paris.

The avoirdupois system (avdp system) is in use in the United Kingdom (UK) and the United States of America (US) :
1 Pound [lb] = 16 Ounces [oz] = 256 Drams [dr] = 7000 Grains [gr]
1 Short Ton [tn] = 2000 Pounds [lb]
1 Long Ton [l.tn] = 2240 Pounds [lb]
1,0 Pound [lb] = 0,45359237 Kilogram [kg]

The Troy system is preferably used for gold, silver and precious stones.
1 Troy Pound [lb]= 12 Troy Ounces [oz] = 240 Pennyweights [pwt] = 5760 Grains [gr]
1,0 Pound [lb] = 0,3732417216 Kilogram [kg]

The Carat [ct] is regarded as weight unit for precious stones. It is derived from the weight of a seed kernel of the carob tree.
In Troy System 1 Carat = 0,2053 Gram.
1875 metric Carat [ct] was introduced:
1 Carat [ct] = 0,2 Gram [g]

The gold carats [ct] is an indication of precious metal alloys. The "Cologne Mark" (233.8g) were divided in gold in 24 parts (carats) and silver in 16 parts (Loth).
14 kt gold are 14 parts of precious metal out of total 24 parts, so 14/24 = 0,583. Nowadays it is calculated in 1000 parts instead of 24 parts. 14 kt gold content corresponds with 585 /1000 gold content.

That no longer in use "hundredweight" [cwt] corresponds in Europe approximately with the "centner" or the "quintal".

In Britain, 112 pounds avoirdupois (50.8023 kg) are  a "hundredweight" or "Long hundredweight". 20 "Long Hundredweights" correspond with a "Long Ton".

In the United States a good correspondence with the centner was in contrast abandoned for the benefit of the decimal system.

100 pounds avoirdupois (45.3592 kilograms) are designated here as a "hundredweight", also known as "Short hundredweight" or "Cental". 20 centals correspond with a "Short Ton".