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Metric Units

The SI metric system is the standard weight measurement system across the majority of the globe, with only the US and a few small countries not using it as their national standard. The base unit of the SI metric system is the kilogram which is based on the International Prototype Kilogram (IPK) held in Sèvres, France.

The kilogram is the only base metric unit to use a prefix and other metric weight units use the standard metric prefixes (centi, deci, milli etc).

Table of Metric Weight Units

Unit Abbreviation As Grams Useful Information
microgram μg 0.000001 Used in food and pharmaceutical labelling
milligram mg 0.001 Used in food and pharmaceutical labelling
centigram cg 0.01 Rarely used
decigram dg 0.1 Rarely used
gram g 1 Grams are commonly used in retail sales
decagram dag 10 Rarely used
hectogram hg 100 Rarely used
kilogram kg 1,000 Metric system base weight unit
megagram Mg 1,000,000 The tonne (metric ton) is 1 megagram
Imperial Units

The avoirdupois weight system is the basis of both the British Imperial and US Customary weight systems. It was first recorded in Britain in the Late 13th or early 14th century and is thought to derive from an old French or old Florentine weight system used by wool merchants.

During the reign of Henry VIII an English statute made the avoirdupois system mandatory and Elizabeth I added the grain of 1/7000th of a pound to the system giving a system that is recognisable as the British Imperial weight units. Although the stone had been part of the avoirdupois system since the 14th Century, it was not formerly incorporated into the British Imperial system until the Weights and Measures Act of 1835 and thus did not make it into the US Customary units.

Table of British Imperial Weight Units

Unit Abbreviation As Kilograms Useful Information
grain gr 0.0000648 Used for precious metals and gunpowder
dram dr 0.0017718 1/16th of an ounce, previously known as the part
ounce oz 0.02835 Often used in cooking measures in both the US and UK
pound lb 0.453592 Avoirdupois weight system base unit
stone st 6.35029 Not part of US customary system
quarter qtr 12.70058 Quarter of a hundredweight, also 2 stone
hundredweight cwt 50.80235 Defined as 8 stone in the British Imperial system
ton t 1016.04691 Also known as the long ton to differentiate it from the US short ton

 

The US Customary weight system was effectively the British system as used in 1776 at the time of American independence with minor modifications made thereafter. The major differences between the US Customary system and the British Imperial system are in weights above the pound, with the US keeping the 100lb hundredweight that was abolished by the British Weights and Measures Act of 1824. The quarter and ton also differ from the British system as they are a quarter of a hundredweight and twenty hundredweight respectively.

Table of US Customary Weight Units

Unit Abbreviation As Kilograms Useful Information
grain gr 0.0000648 Used for precious metals and gunpowder
dram dr 0.0017718 1/16th of an ounce, previously known as the part
ounce oz 0.02835 Often used in cooking measures in both the US and UK
pound lb 0.453592 Avoirdupois weight system base unit
quarter qtr 11.33981 Quarter of a hundredweight, 25lb in the US Customary system
hundredweight cwt 45.35924 Defined as 100lb in the US Customary system
ton t 907.18474 Also known as the short ton to differentiate it from the British long ton

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