Specific Gravity Calculator

What Is Specific Gravity?

“Specific gravity is the ratio of a substance’s density relative to the density of a reference substance.”

Under standard conditions, solids and liquids are typically compared with water at 4°C, which has a density of \[ \rho_\text{water} = 1000 \, \text{kg/m}^3 \]. For gases, the comparison is usually made with dry air, which has a density of \[ \rho_\text{air} = 1.29 \, \text{kg/m}^3 \, (1.29 \, \text{g/L or } 0.0807 \, \text{lb/ft}^3) \].

Formula for Specific Gravity Calculator

Specific gravity is calculated using the following formula:

\[ SG = \frac{\text{Density of Substance}}{\text{Density of Reference Substance}} \]

Or using standard notation with Greek letters:

\[ SG = \frac{\rho_{\text{substance}}}{\rho_{\text{reference}}} \]

For liquids and solids, the reference substance is usually water at 4°C (39°F), where water reaches its maximum density. For gases, dry air is typically used as the reference substance.

How to Calculate Specific Gravity

To calculate the specific gravity of a substance, divide the density of the material by the density of the reference substance (water for liquids/solids, air for gases).

Example:

Assume a sample of aluminum has a density of 2,700 kg/m3. Find its specific gravity relative to water (density = 1,000 kg/m3).

Solution:

Given:

• Density of material: \(\rho_\text{material} = 2700 \, \text{kg/m}^3\)
• Density of water: \(\rho_\text{water} = 1000 \, \text{kg/m}^3\)

Calculation:

\[ SG = \frac{\rho_\text{material}}{\rho_\text{water}} = \frac{2700}{1000} = 2.7 \]

The specific gravity of aluminum is 2.7, indicating that it is 2.7 times denser than water.

Is Specific Gravity Affected by Temperature?

Yes. Specific gravity depends on both temperature and pressure. As temperature increases, the density of the substance generally decreases, which reduces its specific gravity. Objects with a specific gravity of 1 are in equilibrium with water under standard conditions.

Specific Gravity Table for Common Materials