Fluid Density Calculator

The density of a substance is defined as its mass per unit volume:

$$\rho = \frac{m}{V}$$

For fluids, density depends on temperature and pressure. This calculator computes density from measured mass and volume, and also provides a temperature-corrected water density reference using a polynomial approximation valid from 0–100°C at atmospheric pressure:

$$\rho_{\text{water}}(T) \approx 999.84 + 0.0679T - 0.00910T^2 + 1.00 \times 10^{-4}T^3 - 1.12 \times 10^{-6}T^4 + 6.54 \times 10^{-9}T^5$$

where T is in degrees Celsius. Water reaches its maximum density of 999.97 kg/m³ at approximately 3.98°C — an anomaly critical for aquatic life, as ice floats and lakes freeze from the top down.

Key density concepts:

• SI units: kg/m³ is the SI unit. Common alternatives include g/cm³ (= g/mL = kg/L), where 1 g/cm³ = 1000 kg/m³.
• Temperature effects on liquids: Most liquids expand when heated, decreasing density. Water is exceptional — it contracts from 0°C to 4°C before expanding.
• Pressure effects: Liquids are nearly incompressible, so density changes little with pressure. Gases are highly compressible, with density proportional to pressure (ideal gas law).
• Specific gravity: The ratio $$SG = \rho_{\text{fluid}} / \rho_{\text{water}}$$ at the same temperature. A dimensionless quantity that indicates whether the fluid floats (SG < 1) or sinks (SG > 1) in water.

Common fluid densities at 20°C: freshwater ≈ 998 kg/m³, seawater ≈ 1025 kg/m³, mercury ≈ 13,546 kg/m³, ethanol ≈ 789 kg/m³, gasoline ≈ 720 kg/m³, air ≈ 1.2 kg/m³.

The calculated density tells you the mass per unit volume of your fluid. Compare with known values: water is about 998 kg/m³ at 20°C, and the specific gravity indicates the ratio relative to water at the given temperature. An SG greater than 1 means the fluid is denser than water; less than 1 means it is lighter. The water density reference adjusts automatically with your temperature input.