The Litre Is Not an Official SI Unit
A litre is a metric unit of volume. It is accepted for use with the metric system but is not one of its base or derived units.
A liter is a metric unit of volume equal to one thousand cubic centimetres. Technically it is not part of the International System of Units: the SI unit of volume is the cubic metre, and the litre is merely *accepted for use* alongside it because it is so entrenched. A litre is one thousandth of a cubic metre. Both *l* and *L* are permitted as symbols, with the capital preferred in some countries because a lower-case l looks like the digit one.
- A unit of volume. *Two litres of water.*
- Litre — the British spelling. *A litre.*
- Millilitre — a thousandth. *500 millilitres.*
- Cubic metre — the SI unit. *One cubic metre.*
- Symbol — l or L. *5 L.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun (US) | liter | One liter. |
| Noun (UK) | litre | One litre. |
| Plural | litres | Two litres. |
| Symbol | L | 5 L. |
| Greek | litra | A unit of weight. |
- The bottle holds two litres.Volume.
- A litre is a thousandth of a cubic metre.Relation.
- Liter is the American spelling.Spelling.
Metric units accepted but not SI
- Litre — volume, alongside the cubic metre
- Tonne — mass, alongside the kilogram
- Hectare — area, alongside the square metre
- Minute, hour, day — time, alongside the second
- All are permitted because everyday use demands them
French *litre*, from *litron*, an old measure, from Medieval Latin *litra*, from Greek *litra*, a unit of weight.
Is the litre an SI unit?
No. The SI unit of volume is the cubic metre. The litre is accepted for use with SI because it is so widely used.
Should the symbol be l or L?
Both are allowed. The capital L is often preferred because a lower-case l can be mistaken for the digit one.