The specific gravity calculator computes the ratio of a substance's density to water's density (1000 kg/m³ or 1 g/cm³). SG > 1 sinks; SG < 1 floats. Supports g/cm³, kg/m³, and lb/ft³ inputs.
Specific Gravity Calculator
How to Use the Specific Gravity Calculator
Specific gravity (SG) is the ratio of a substance's density to the density of water at 4°C (1 g/cm³ = 1000 kg/m³ = 62.428 lb/ft³). It is dimensionless.
Formula
SG = ρ_substance / ρ_water. For g/cm³: SG = density (since water = 1). For kg/m³: SG = density / 1000. For lb/ft³: SG = density / 62.428.
Float or Sink?
An object floats in water if SG < 1. It sinks if SG > 1. Ice has SG ≈ 0.917, so it floats. Steel ≈ 7.8, so it sinks. A hollow steel ship floats because the average density of the hull + air is less than 1.
Brewing Hydrometers
Brewers use specific gravity to measure sugar content in wort and finished beer. Original gravity (OG) of beer is typically 1.040–1.080. Final gravity (FG) after fermentation is 1.005–1.015. ABV ≈ (OG − FG) × 131.25.
Reference Values
Water = 1.000. Ethanol = 0.789. Ice = 0.917. Olive oil = 0.91. Sea water ≈ 1.025. Concrete ≈ 2.3. Iron ≈ 7.87. Lead ≈ 11.35. Gold ≈ 19.32. Mercury = 13.55.
FAQ
What is specific gravity?
Specific gravity (SG) = density of substance / density of reference (usually water at 4°C, 1000 kg/m³). It's dimensionless. SG > 1 means denser than water (sinks). SG < 1 means less dense than water (floats). Gold SG ≈ 19.3. Ice SG ≈ 0.917. Steel SG ≈ 7.8. Wood varies: balsa 0.12, oak 0.75.
What is the difference between density and specific gravity?
Density has units (kg/m³, g/cm³, lb/ft³). Specific gravity is dimensionless — it's a ratio. In CGS units, density in g/cm³ numerically equals specific gravity (since water = 1 g/cm³). But in SI units, density in kg/m³ must be divided by 1000 to get specific gravity.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
How is specific gravity used in brewing?
Brewers measure original gravity (OG) and final gravity (FG) of beer with a hydrometer. The difference indicates how much sugar fermented into alcohol. SG 1.050 OG and 1.010 FG gives ABV ≈ (1.050 − 1.010) × 131.25 = 5.25%. Specific gravity > 1 for liquids denser than water.