The Gram Was Defined by a Cubic Centimetre of Water
A gram is a metric unit of mass. Its original definition tied it directly to water.
A gram is a metric unit of mass, one thousandth of a kilogram. It was originally defined as the mass of one cubic centimetre of water at its densest point, which tied length, volume and mass into one system — that neatness is why a litre of water still weighs almost exactly a kilogram. The kilogram was redefined in 2019 in terms of a fundamental physical constant, ending the last use of a physical object as a standard unit.
- A unit of mass. *Five hundred grams.*
- Kilogram — a thousand grams. *A kilogram.*
- Gramme — the older British spelling. *Gramme.*
- Defined by water. *Originally.*
- Greek — *gramma*, a small weight. *The root.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | gram | A gram. |
| Plural | grams | Grams. |
| Variant | gramme | A gramme. |
| Compound | kilogram | A kilogram. |
| Symbol | g | 500 g. |
- Add two hundred grams of flour.Cooking.
- A litre of water is about a kilogram.Fact.
- The kilogram was redefined in 2019.History.
How the metric system linked its units
- The metre was defined from the size of the Earth
- The litre was a cubic decimetre
- The gram was a cubic centimetre of water
- So length, volume and mass locked together
- In 2019 the kilogram was redefined using the Planck constant
French *gramme*, from late Latin *gramma*, a small weight, from Greek *gramma*, a letter or small measure.
How was the gram originally defined?
As the mass of one cubic centimetre of water at its densest point, linking mass directly to length and volume.
Why does a litre of water weigh a kilogram?
Because the metric system was designed that way. The definition of mass was taken from the mass of water.