The density of pure water, at its point of maximum density (4°C), is about
1.000 kg/m³
Water has historically been used as the reference for defining the gram and the kilogram, which is why its density comes out to an almost exact number: 1,000 kg/m³ (= 1 g/cm³) at 4°C, the temperature at which water reaches its maximum density. At different temperatures, the density of water varies slightly: for example, it's about 998 kg/m³ at 20°C (room temperature) and about 958 kg/m³ near the boiling point.
Density is always calculated as the ratio between mass and volume:
Applied to water, this means that 1 liter (0.001 m³) of water weighs about:
The density of water is one of the most searched values in physics and chemistry, both for educational purposes (it's one of the first examples used to explain the concept of density) and for practical calculations, such as estimating the weight of a volume of water for aquarium projects, irrigation, or hydraulic engineering.