Specific Gravity Calculator

What is Specific Gravity?

Specific gravity ($SG$), also known as relative density, is a dimensionless quantity that represents the ratio of the density of a substance to the density of a reference fluid (usually water at 4 °C for liquids and solids, or air for gases). It tells us how many times denser the substance is compared to the reference. In practical terms, specific gravity determines whether an object will float or sink in water. For the inverse concept, try our Specific Volume Calculator.

Specific Gravity Formulas

Depending on the available measurements, specific gravity can be calculated using density or specific weight:

1. Density Ratio Form

$$SG = \frac{\rho_{\text{substance}}}{\rho_{\text{reference}}}$$

Where:

• $\rho_{\text{substance}}$ = Density of the substance
• $\rho_{\text{reference}}$ = Density of the reference fluid (e.g., $1,000\text{ kg/m}^3$ for water at 4 °C)

2. Specific Weight Ratio Form

$$SG = \frac{\gamma_{\text{substance}}}{\gamma_{\text{reference}}}$$

Where:

• $\gamma_{\text{substance}}$ = Specific weight of the substance
• $\gamma_{\text{reference}}$ = Specific weight of the reference fluid (e.g., $9.807\text{ kN/m}^3$ for water)

Specific Gravity of Common Materials

Below is a reference table containing the specific gravity values of common materials relative to water at 4 °C.