Metric system

A metric system is a system of units for measurement developed in late 18th century France with decimal multipliers. In the early metric system there were two fundamental or base units, the metre and the kilogram, for length and mass. Other units were derived from these two fundamental units.

Spelling variations

Several nations, notably the United States, typically use the spellings 'meter' and 'liter' instead of 'metre' and 'litre'. This is in keeping with standard American English spelling (for example, Americans also use 'center' rather than 'centre,' using the latter only rarely for its stylistic implications; see also American and British English differences). In addition, the official US spelling for the SI prefix 'deca' is 'deka'.

Related Topics:
United States - American English - American and British English differences - SI prefix

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The US government has approved these spellings for official use. In scientific contexts only the symbols are used; since these are universally the same, the differences do not arise in practice in scientific use.

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The unit 'gram' is also sometimes spelled 'gramme' in English-speaking countries other than the United States, though that is an older spelling and use is declining.

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