Enter a temperature and optional salinity to calculate the density of water in your preferred units. The Water Density Calculator returns the water density in kg/m³, g/mL, and lb/ft³, plus the specific gravity — showing how temperature and salt content affect water's mass per unit volume.
Water Density
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Density (kg/m³)
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Density (g/mL)
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Density (lb/ft³)
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Specific Gravity
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Temperature (°C)
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The density of water is the ratio of its mass to its volume (ρ = m/V). At 4°C, pure water reaches its maximum density of approximately 999.97 kg/m³ (or very close to 1 g/mL). Density decreases both above and below this temperature due to water's unique molecular structure.
As water heats up, its molecules move faster and spread apart, reducing density. As it cools below 4°C, water forms a hexagonal crystalline structure (ice) that is actually less dense than liquid water. This is why ice floats — a rare property among substances.
Seawater with a typical salinity of about 35 ppt has a density of approximately 1025 kg/m³ at 20°C — about 2.5% denser than fresh water. The more dissolved salts, the higher the density. The Dead Sea, with extreme salinity (~340 ppt), has a density of around 1240 kg/m³.
A fresh egg has a density of about 1.03–1.07 g/mL. In fresh water (~1.00 g/mL), the egg sinks because it is denser than the water. In heavily salted water (density above ~1.07 g/mL), the egg floats. This is a common test for egg freshness — as eggs age, air pockets form inside, reducing their density.
Water density is most commonly expressed in kg/m³ (SI unit), g/mL (or g/cm³, which are equivalent), and lb/ft³ (imperial). The values 1000 kg/m³, 1 g/mL, and 62.43 lb/ft³ all represent approximately the same density of pure water at 4°C.
Specific gravity is the ratio of a substance's density to the density of pure water at 4°C (999.97 kg/m³). Pure water has a specific gravity of exactly 1.000. Salt water above 1.000 is denser than pure water. Specific gravity is dimensionless and is widely used in aquarium and marine science.
Water is nearly incompressible, so pressure has a relatively small effect on its density compared to temperature and salinity. However, at extreme depths in the ocean (thousands of meters), pressure can increase water density by about 4–5%. For most practical surface-level calculations, pressure effects are ignored.
Pure water reaches its maximum density of approximately 999.97 kg/m³ at 3.98°C (about 4°C). This is why lakes freeze from the top down in winter — the denser 4°C water sinks to the bottom, while the less-dense near-freezing water rises to the surface and eventually freezes.