Specific Gravity Calculator

Specific gravity (SG) is a dimensionless ratio that compares the density of a substance to the density of a reference substance — typically water at 4°C (39.2°F), which has a density of exactly 1,000 kg/m³.

The Core Formula:

SG = ρ_substance / ρ_reference

For liquids and solids (referenced to water):

SG = ρ_material / 1,000 kg/m³

For gases, the reference is air at STP (1.225 kg/m³).

Using Archimedes’ Principle (for irregular solids):

SG = Weight in Air / (Weight in Air − Weight in Water)

Worked Example 1 — Liquid sample:

• A 500 mL oil sample weighs 430 g
• Density = 430 g / 500 mL = 0.860 g/cm³
• SG = 0.860 / 1.000 = 0.860 (floats on water — SG < 1)

Worked Example 2 — Irregular solid:

• A rock weighs 250 g in air and 155 g submerged in water
• Buoyant force = 250 − 155 = 95 g equivalent
• SG = 250 / 95 = 2.63 (similar to granite)

Reference Table:

Applications: Used in brewing (alcohol content), mining (ore separation), geology (mineral identification), and fluid dynamics. A hydrometer directly measures SG of liquids.