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.
Tips
- Stress is force per area; strain is a dimensionless ratio.
- Material presets fill in typical values – check a datasheet for design work.
- Keep stress units consistent: 1 MPa = 1 N/mm².
- Elastic formulas only apply below the yield point.
Common mistakes to avoid
- Mixing MPa and GPa when using Young’s modulus.
- Using engineering strain where true strain is needed.
- Treating these results as a substitute for a qualified structural design.
Inputs explained
| Field | What to enter |
|---|---|
| Substance | Choose one: Water (4 °C), Seawater, Ice, Air (sea level, 15 °C) … |
| Substance density | Units: kg/m³, g/cm³, g/mL, lb/ft³, lb/in³ |
| Reference substance | Choose 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 gravity |
|---|---|
| 525 | 0.917 |
| 787.5 | 0.917 |
| 1,050 | 0.917 |
| 1,312.5 | 0.917 |
| 1,575 | 0.917 |
| 2,100 | 0.917 |
Formula
SG = ρ_substance / ρ_reference, API gravity = 141.5/SG − 131.5Worked 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.
Frequently asked questions
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.
What formula does the Specific Gravity Calculator use?
SG = ρ_substance / ρ_reference, API gravity = 141.5/SG − 131.5.