# What is the specific gravity?

Computes specific gravity, the density of a substance divided by the density of water, from its density or by weighing an object in air and in water, with its density in g/cm³, kg/m³ and lb/ft³.

- Page: https://www.acalculator.org/physics/specific-gravity-calculator
- JSON spec: https://www.acalculator.org/physics/specific-gravity-calculator.json
- Version: bcaf71c7a350

## Default answer

Example with the default inputs (Method From density, Density of the substance 19.32 g/cm³, Density of water (reference) 1 g/cm³): The specific gravity is 19.32, a density of 19.32 g/cm³.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| m | Method | From a known density, or by weighing the object in air and then in water. |
| rho | Density of the substance | The density of the substance or object. |
| ma | Mass in air | The mass (or weight) of the object weighed in air. |
| mw | Apparent mass in water | The reading with the object hanging fully under water; it must be less than the mass in air. |
| ref | Density of water (reference) | The density of the reference liquid: water at 4 °C is 1 g/cm³ (1,000 kg/m³). |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| sg | Specific gravity | The density of the substance ÷ the density of water; it has no unit. |
| gcc | Density (g/cm³) | Specific gravity × the reference density, in grams per cubic centimeter. |
| kgm3 | Density (kg/m³) | The same density in kilograms per cubic meter. |
| lbft3 | Density (lb/ft³) | The same density in pounds per cubic foot. |
| displaced | Mass of water displaced (g) | Mass in air − apparent mass in water. |
| volume | Volume of the object (cm³) | Mass of water displaced ÷ the density of water. |

## Method

Specific gravity = ρ ÷ ρ_water. By weighing: specific gravity = m_air ÷ (m_air − m_water), since m_air − m_water is the mass of water displaced; density = specific gravity × ρ_water.

## Assumptions

- The reference is water at 4 °C, 1.000 g/cm³ (1,000 kg/m³), unless you type another reference density.
- When weighing, the object is fully under water, holds no air, and does not absorb water; the apparent mass in water is the scale reading then.
- Units convert exactly: 1 g/cm³ = 1,000 kg/m³; 1 lb = 0.45359237 kg; 1 ft³ = 0.028316846592 m³; 1 gal = 0.003785411784 m³.

## Worked examples

1. m = density, rho = 19,320, ref = 1,000 gives sg = 19.32, gcc = 19.32, kgm3 = 19,320, lbft3 = 1,206.108198. Source: OpenStax, College Physics 2e, §11.2 Density, Table 11.1 (water at 4 °C 1.000, gold 19.32, mercury 13.6, in 10³ kg/m³), https://openstax.org/books/college-physics-2e/pages/11-2-density (retrieved 2026-10-18); OpenStax, College Physics 2e, §11.7 Archimedes’ Principle (specific gravity = ρ̄ ÷ ρw, the density of water at 4.00 °C; apparent mass loss = mass of fluid displaced; Example 11.10: 8.630 g in air, 7.800 g in water, 0.830 cm³, 10.4 g/cm³), https://openstax.org/books/college-physics-2e/pages/11-7-archimedes-principle (retrieved 2026-10-18).
2. m = weigh, ma = 0.00863, mw = 0.0078, ref = 1,000 gives sg = 10.39759, kgm3 = 10,397.590361, displaced = 0.83, volume = 0.83. Source: OpenStax, College Physics 2e, §11.7 Archimedes’ Principle (specific gravity = ρ̄ ÷ ρw, the density of water at 4.00 °C; apparent mass loss = mass of fluid displaced; Example 11.10: 8.630 g in air, 7.800 g in water, 0.830 cm³, 10.4 g/cm³), https://openstax.org/books/college-physics-2e/pages/11-7-archimedes-principle (retrieved 2026-10-18).
3. m = density, rho = 999.552115, ref = 1,000 gives sg = 0.999552, lbft3 = 62.4. Source: OpenStax, College Physics 2e, §11.7 Archimedes’ Principle (specific gravity = ρ̄ ÷ ρw, the density of water at 4.00 °C; apparent mass loss = mass of fluid displaced; Example 11.10: 8.630 g in air, 7.800 g in water, 0.830 cm³, 10.4 g/cm³), https://openstax.org/books/college-physics-2e/pages/11-7-archimedes-principle (retrieved 2026-10-18); NIST SP 811, Appendix B.8 (1 lb = 0.45359237 kg, 1 ft³ = 0.028316846592 m³).
4. m = density, rho = 13,600, ref = 1,000 gives sg = 13.6, gcc = 13.6. Source: OpenStax, College Physics 2e, §11.2 Density, Table 11.1 (water at 4 °C 1.000, gold 19.32, mercury 13.6, in 10³ kg/m³), https://openstax.org/books/college-physics-2e/pages/11-2-density (retrieved 2026-10-18).

## FAQ

### What is specific gravity?

It is the density of a substance divided by the density of a reference liquid, usually water. Because the two densities share a unit, specific gravity has no unit. Gold, at 19.32 g/cm³, has a specific gravity of 19.32.

### How do I calculate specific gravity from density?

Divide the density by the density of water at 4 °C, 1.000 g/cm³ or 1,000 kg/m³, in the same unit. Mercury at 13.6 g/cm³ has a specific gravity of 13.6 ÷ 1.000 = 13.6.

### How do I find specific gravity by weighing in water?

Weigh the object in air, then hanging fully under water. The difference is the mass of water it pushes aside (Archimedes’ principle). Specific gravity = mass in air ÷ (mass in air − mass in water). A coin of 8.630 g that reads 7.800 g in water has 8.630 ÷ 0.830 = 10.4.

### Is specific gravity the same as density?

Not quite. Specific gravity is a ratio with no unit, while density has units. Against water at 1 g/cm³, the specific gravity has the same number as the density in g/cm³, so 2.7 g/cm³ aluminum has a specific gravity of 2.7.

### What does a specific gravity below 1 mean?

The substance is less dense than water, so a solid piece of it floats. Above 1 it sinks. Water itself has a specific gravity of 1.

### Can I use a reference other than water?

Yes. Type the density of the reference liquid in place of water’s, for example water at the temperature you measured at. Water at 4 °C, 1.000 g/cm³, is the usual reference.

## Sources

- OpenStax, College Physics 2e, §11.7 Archimedes’ Principle: specific gravity is the ratio of the density of an object to a fluid (usually water), specific gravity = ρ̄ ÷ ρw with ρw the density of water at 4.00 °C (Eq. 11.40); apparent mass loss = mass of fluid displaced (Eq. 11.45); Example 11.10, Is the Coin Authentic? (8.630 g in air, 7.800 g in water, 0.830 cm³, 10.4 g/cm³). https://openstax.org/books/college-physics-2e/pages/11-7-archimedes-principle (retrieved 2026-10-18)
- OpenStax, College Physics 2e, §11.2 Density, Table 11.1 Densities of Various Substances: water (4 °C) 1.000, gold 19.32, aluminum 2.7, mercury 13.6, in 10³ kg/m³ or g/mL. https://openstax.org/books/college-physics-2e/pages/11-2-density (retrieved 2026-10-18)