# Specific Gravity Calculator

URL: https://speedycalculator.com/calculators/physics/specific-gravity/
Last updated: 2026-10-30

> The specific gravity calculator finds the specific gravity (relative density) of a substance compared with water or air, and the API gravity for petroleum liquids.

## Inputs

- Substance
- Substance density (kg/m³, g/cm³, g/mL, lb/ft³, lb/in³)
- Reference substance

## Results

- Specific gravity
- API gravity (vs. water at 60 °F)
- In water

## Formula

```
SG = ρ_substance / ρ_reference,  API gravity = 141.5/SG − 131.5
```

## Explanation

Specific gravity compares a material's density with water's. If SG is above 1, it sinks in water; below 1, it floats. Brewers use it to track fermentation, gemologists to identify stones and the oil industry uses API gravity.

### How to use the Specific Gravity Calculator

- **Substance**
- **Substance density**
- **Reference substance**

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

### How it works

Enter the density of the substance (or pick one) and choose the reference.

### Inputs explained

FieldWhat to enterSubstanceChoose one: Water (4 °C), Seawater, Ice, Air (sea level, 15 °C) …Substance densityUnits: kg/m³, g/cm³, g/mL, lb/ft³, lb/in³Reference substanceChoose one: Water at 4 °C (999.97 kg/m³), Water at 20 °C (998.2 kg/m³), Water at 60 °F (999.0 kg/m³), Air at 15 °C (1.225 kg/m³)

### What each result means

- **Specific gravity** = [r]÷[Reference substance]
- **API gravity (vs. water at 60 °F)** = 141.5÷([r]÷999.016) - 131.5

### Example values

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

Substance density (kg/m³)Specific gravity5250.917787.50.9171,0500.9171,312.50.9171,5750.9172,1000.917

## Worked example

Inputs — Substance: Ice; Reference substance: Water at 4 °C (999.97 kg/m³).

Results — **Specific gravity = 0.91703**; API gravity (vs. water at 60 °F) = 22.6557 °API; In water = Floats.

## Key terms

- **Relative density**: Another name for specific gravity.

## FAQ

**What is the specific gravity of water?**
1 by definition (at the reference temperature).

**Does specific gravity have units?**
No – it is a ratio.

**What is a light crude oil?**
API gravity above about 31.1°.

**How do brewers use SG?**
Falling gravity shows sugar being turned into alcohol.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)
- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)