Specific Gravity Calculator
Convert between specific gravity and density in both directions. Enter a density (kg/m³, g/cm³, or lb/ft³) to get its specific gravity, or enter a specific gravity to get the density — all referenced to water at 1000 kg/m³.
Example: with I want to Density → specific gravity · Value 1025 · Density unit (for density input) kg/m³ → Specific gravity: 1.0250.
- Density (metric)1,025 kg/m³ (1.0250 g/cm³)
- Density (lb/ft³)63.99 lb/ft³
Computed by the calculator below using its default values. Change any input to see your own numbers.
Specific gravity is just density measured in units of water: divide by 1000 kg/m³. An SG of 1.03 means 3% denser than water — so it sinks slowly.
Specific gravity versus density
Specific gravity is a density expressed relative to a reference — for liquids and solids, water at 1000 kg/m³. Divide a substance's density by water's and the units cancel, leaving a bare number: aluminum at 2700 kg/m³ has a specific gravity of 2.7. Because it is dimensionless, specific gravity reads the same whether the original density was in kg/m³, g/cm³, or lb/ft³, which is exactly why hydrometers and lab references use it.
The tie to floating is immediate: anything with a specific gravity below 1 floats in water, and anything above 1 sinks. Ice at 0.92 rides just above the surface; seawater at about 1.025 is why swimmers are a touch more buoyant in the ocean. To recover a density from a specific gravity, multiply back by the reference: SG 0.79 gasoline is 790 kg/m³.
How it’s calculated
Specific gravity = substance density / reference density, with the reference taken as water at 1000 kg/m³. Density inputs convert to kg/m³ (g/cm³ ×1000, lb/ft³ ×16.018463) before dividing. Reverse mode multiplies specific gravity by 1000 to get kg/m³, then shows g/cm³ (÷1000) and lb/ft³ (×0.0624280).
Uses water at 1000 kg/m³ (its density near 4 °C) as the reference. Water at 20–25 °C is about 997–998 kg/m³, so tighten the reference for lab-grade work.
Specific gravity of common substances
| Substance | Density (kg/m³) | Specific gravity |
|---|---|---|
| Gasoline | 740 | 0.74 |
| Ice | 917 | 0.92 |
| Water | 1000 | 1.00 |
| Seawater | 1025 | 1.03 |
| Aluminum | 2700 | 2.70 |
| Mercury | 13534 | 13.53 |
Computed as density ÷ 1000 kg/m³; representative densities, rounded.
Common mistakes
- Forgetting to convert g/cm³ to kg/m³ — 1 g/cm³ equals 1000 kg/m³, a factor easy to drop.
- Using water at 1000 vs 998 kg/m³ interchangeably in precise work; the reference temperature matters.
- Reading specific gravity as a percentage; SG 1.03 is 3% denser than water, not 103% of something arbitrary.
- Comparing a gas's specific gravity to water — gases are referenced to air, not water.
Frequently asked questions
What is the specific gravity formula?
Specific gravity = density of the substance ÷ density of water (1000 kg/m³). The result is a dimensionless number, so an SG of 2.7 means 2.7 times as dense as water.
How do I convert specific gravity to density?
Multiply specific gravity by the reference density. Using water at 1000 kg/m³, an SG of 0.79 gives 790 kg/m³, or 0.79 g/cm³, or about 49.3 lb/ft³.
What specific gravity floats in water?
Anything below 1.0 floats and anything above 1.0 sinks. Ice at 0.92 floats; most metals, with SG well above 1, sink.
Why is specific gravity dimensionless?
It is a ratio of two densities in the same units, so the units cancel. That makes it read the same regardless of whether you started in metric or imperial units.