# Water Density Calculator

URL: https://speedycalculator.com/calculators/physics/water-density/
Last updated: 2026-10-30

> The water density calculator finds the density of fresh or salty water at a given temperature, salinity and pressure, and whether an object of a given density floats in it.

## Inputs

- Temperature (°C, °F, K)
- Salinity (g/kg)
- Gauge pressure (bar, MPa, psi, kPa)
- Object density (optional) (kg/m³, g/cm³, g/mL, lb/ft³, lb/in³)

## Results

- Water density
- Specific gravity (vs. 4 °C fresh water)
- The object

## Formula

```
Fresh water (Tanaka 2001): ρ = 999.975·[1 − (T − 3.983)²(T + 301.797)/(522528.9·(T + 69.349))]
Salinity (UNESCO EOS-80 terms) and compressibility ≈ 4.6 × 10⁻¹⁰ Pa⁻¹ are added
```

## Explanation

Water is densest at about 4 °C, which is why lakes freeze from the top and fish survive the winter below. Dissolved salt makes seawater about 2.5% denser, and pressure squeezes it slightly more in the deep ocean.

### How to use the Water Density Calculator

- **Temperature**
- **Salinity (g/kg)**
- **Gauge pressure**
- **Object density (optional)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the temperature, salinity (35 g/kg for typical seawater) and gauge pressure, and optionally the density of an object.

### Inputs explained

FieldWhat to enterTemperatureUnits: °C, °F, KSalinity (g/kg)A numberGauge pressureUnits: bar, MPa, psi, kPaObject density (optional)Units: kg/m³, g/cm³, g/mL, lb/ft³, lb/in³

### What each result means

- **Water density** = [rs]×(1 + 4.6e-10×[Gauge pressure])
- **Specific gravity (vs. 4 °C fresh water)** = [Water density]÷999.97

### Example values

How the main result changes when **Temperature** changes and everything else stays at the example values above:

Temperature (°C)Water density (kg/m³)10999.702715999.102620998.206725997.04730995.648840992.2152

## Worked example

Inputs — Temperature: 20 °C; Salinity (g/kg): 0; Gauge pressure: 0 bar; Object density (optional): 1,000 kg/m³.

Results — **Water density = 998.206746 kg/m³**; Specific gravity (vs. 4 °C fresh water) = 0.998237; The object = Sinks.

## Key terms

- **Salinity**: Mass of dissolved salts per kilogram of seawater.

## FAQ

**At what temperature is water densest?**
About 3.98 °C (999.97 kg/m³).

**How dense is seawater?**
About 1,025 kg/m³ at the surface.

**Does pressure change water density much?**
Only slightly – about 0.46% per 100 bar.

**Why does ice float?**
Ice is about 9% less dense than liquid water.


## Sources

- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)
- [UNESCO – Algorithms for computation of fundamental properties of seawater (1983)](https://unesdoc.unesco.org/ark:/48223/pf0000059832)