About the Specific Gravity Calculator
This specific gravity calculator finds the specific gravity (relative density) of a liquid or solid — the ratio of its density to the density of water — and converts it to the other scales people actually use. You can start from a measured density, from a hydrostatic weighing (mass in air and apparent mass submerged in water), or from a sugar (°Brix), brewing (°Plato) or petroleum (°API) reading.
It is useful for homebrewers checking wort and must, winemakers and food technologists working with Brix, lab staff identifying materials, jewellers testing metals, and anyone converting a data-sheet SG into density. Results include density in g/cm³, kg/m³ and US lb/gal, plus the equivalent Brix, Plato and API gravity.
Specific gravity depends on the reference temperature of the water. For density and weighing inputs, choose water at 4 °C (maximum density, 0.999975 g/cm³), 60 °F (0.999016 g/cm³) or 20 °C (0.998207 g/cm³). Brix and Plato readings are always treated as SG 20/20 °C and API gravity as SG 60/60 °F, the conventions those scales are defined on. The Brix and Plato conversions are standard polynomial approximations valid for sugar solutions up to about 40 °Brix.
With the default inputs, the specific gravity is 1.261. Change any value above to recalculate instantly.
How to use the specific gravity calculator
- 1Choose what you measured: density, weights in air and water, Brix, Plato or API.
- 2Enter the reading and, for density, its unit.
- 3For density or weighing inputs, pick the reference water temperature that matches your standard.
- 4Read the specific gravity and the converted densities and scales.
Formula and method
Specific gravity is the ratio of a substance’s density to that of water at a stated reference temperature, so it has no units. Density is recovered by multiplying SG by the reference water density. In the hydrostatic method (Archimedes’ principle) the loss of weight when the object is submerged equals the weight of water displaced, so SG = weight in air ÷ (weight in air − apparent weight in water).
Brix (percent sucrose by mass) and Plato (percent extract in wort) are related to SG by empirical cubic polynomials; Plato uses −616.868 + 1111.14·SG − 630.272·SG² + 135.997·SG³. The calculator inverts these numerically when you start from a Brix or Plato reading. API gravity is defined by the American Petroleum Institute at 60 °F, with water at 10 °API.
- SG
- Specific gravity (dimensionless)
- ρ
- Density (g/cm³)
- W_air, W_water
- Weight in air and apparent weight fully submerged in water
- °Bx, °P, °API
- Brix, Plato and API gravity scales
Worked examples
Glycerin with density 1.261 g/cm³
Dividing 1.261 g/cm³ by the density of water at 4 °C (0.999975 g/cm³) gives SG = 1.2610. In US units that is 1.261 × 8.345 = 10.52 lb per gallon.
Hydrostatic weighing: 50 g in air, 31.5 g in water
The object loses 50 − 31.5 = 18.5 g when submerged, the weight of the water it displaces. SG = 50 ÷ 18.5 = 2.70, matching aluminium.
Wort at 12 °Brix
Solving the Brix polynomial for 12 °Bx gives SG ≈ 1.0484 (often written 1.048 or "48 gravity points"). Brix and Plato are almost identical at brewing strengths, so the equivalent Plato is also about 12.0.
Crude oil at 35 °API
SG = 141.5 ÷ (35 + 131.5) = 0.8498 at 60 °F. Multiplying by the density of water at 60 °F (0.999016 g/cm³) gives about 849 kg/m³ — a light crude.
Frequently asked questions
What is specific gravity?+
Specific gravity is the density of a substance divided by the density of water at a reference temperature. Because it is a ratio it has no units: an SG of 1.26 means the material is 1.26 times as dense as water.
How do I convert specific gravity to density?+
Multiply the SG by the density of the reference water. With water at 4 °C (0.999975 g/cm³) the density in g/cm³ is essentially equal to the SG; for kg/m³ multiply by about 1,000, and for US lb/gal multiply by 8.345.
How do I convert Brix to specific gravity?+
A quick approximation is SG ≈ 1 + Brix ÷ (258.6 − 0.88 × Brix). This calculator solves the more accurate cubic polynomial instead; 12 °Brix is about 1.048 and 20 °Brix about 1.083.
What is the difference between specific gravity and API gravity?+
API gravity is an inverted scale used for petroleum: °API = 141.5 ÷ SG − 131.5 at 60 °F. Higher API means a lighter oil; water is 10 °API, and oils above 10 °API float on water.
Why does the reference temperature matter?+
Water density changes with temperature — 0.999975 g/cm³ at 4 °C but 0.998207 g/cm³ at 20 °C — so the same sample gives slightly different SG values. Standards state both temperatures, such as SG 20/20 °C or 60/60 °F.