Water Density Calculator

Will it float or sink? Use the water density calculator, which takes temperature, salinity, and pressure into account, to answer the question.

Density998.2041 kg/m³0.998204 g/cm³ at 20 °C

Dynamic viscosity1.0017 mPa·s1.00175 centipoise

Kinematic viscosity1.0036e-6 m²/s1.00355 centistokes

Specific weight9,789.04 N/m³

Maximum density, at about 4 °C999.972 kg/m³water is DENSER at 4 °C than at 0 °C (999.84) — the anomaly that makes ice float and lets lakes freeze from the top down while staying liquid beneath

Against the 4 °C maximum-0.1768%

Viscosity at 80 °C350.9933 µPa·s2.854× less viscous than at 20 °C — viscosity falls steeply with warming, which is why hot water flows so much more freely through fine passages

API gravity34.971°141.5/SG − 131.5 — note it runs BACKWARDS to density, so a higher API number means a lighter oil

Classificationlight crudewater itself is exactly 10° API, which is the float-or-sink boundary

Density of that fluid849.16 kg/m³API gravity is referenced to water at 60 °F

Moisture content, wet basis20%water ÷ total mass — the convention in food and agriculture

Moisture content, dry basis25%water ÷ DRY mass — the convention in timber and soil science, and it can exceed 100%

Water mass50 g

Why the two bases matterthey are not interchangeablea timber moisture content of 100% dry-basis is 50% wet-basis — quoting one as the other is a large error, and the dry basis is unbounded

The formula

ρ and µ against temperature; API gravity = 141.5/SG − 131.5

Water is densest at 4 °C

Almost every liquid grows denser as it cools, right down to freezing. Water reverses below about 4 °C and becomes lighter again, so ice floats and a freezing lake forms a lid while staying liquid underneath. Aquatic life survives winter because of this single anomaly, and the fits used here reproduce the maximum rather than assuming a monotonic decline.

Viscosity falls far more steeply with temperature than density does — roughly threefold between 20 °C and 80 °C, against a density change under 3%. That is why hot water flows so much more readily through narrow passages, and why viscosity must be evaluated at the working temperature in any Reynolds or pressure-drop calculation.

API gravity runs backwards to density: a higher number means a lighter oil. Water sits at exactly 10°, which conveniently marks the float-or-sink boundary — anything below 10° API is denser than water.

Moisture content has two incompatible conventions. Wet basis divides by total mass and cannot exceed 100%; dry basis divides by dry mass and can. Timber at 100% dry-basis moisture is 50% water by weight, so quoting one convention as the other is a factor-of-two class of error — and both are in routine use in different industries.