Specific Gravity Calculator
Use the same units for both densities (e.g. kg/m3 or g/cm3). The ratio is dimensionless.
Specific gravity, also called relative density, expresses how dense a material is compared with a reference fluid rather than as an absolute figure. Whereas density carries units (mass per unit volume), specific gravity is a pure dimensionless ratio: divide the substance density by the reference density and the units cancel out. Water at 1000 kg/m3 (equivalently 1.0 g/cm3) is the usual reference, so a value above 1 means the material is heavier than water and will sink, while a value below 1 means it is lighter and will float.
Formula
SG = rho_substance / rho_reference
- SG
- Specific gravity, a dimensionless ratio with no units
- rho_substance
- Density of the material being tested
- rho_reference
- Density of the reference fluid, usually water (1000 kg/m3 or 1.0 g/cm3)
How it works
- Enter the density of your substance and the density of the reference fluid using the same units for both, then read off the dimensionless ratio.
- The engine divides the substance density by the reference density, rounds the ratio to four decimal places, and classifies the result as Sinks (above 1), Floats (below 1), or Neutral (exactly 1).
- Because both inputs share units, the answer is the same whether you work in kg/m3, g/cm3, or any other consistent pair.
Worked example
A sample of vegetable oil has a density of 920 kg/m3 and is compared against water at 1000 kg/m3.
- Divide the oil density by the water density: 920 / 1000.
- The ratio works out to 0.92, which is rounded to four decimal places.
- Since 0.92 is below 1, the oil is lighter than water.
Specific gravity = 0.92 (Floats), so the oil layers on top of water.
Frequently asked questions
- Why does specific gravity have no units?
- It is a ratio of two densities measured in the same units, so the units divide out and leave a bare number. That is precisely what separates it from density, which always reports mass per unit volume.
- Can I use a reference fluid other than water?
- Yes. Water is the default for liquids and solids, but for gases air is common. Just type the reference fluid density into the second field, keeping it in the same units as the substance density.
- What does a specific gravity above 1 tell me?
- A ratio greater than 1 means the substance is denser than the reference fluid, so it sinks in it. Below 1 it floats, and exactly 1 means it is neutrally buoyant and neither rises nor settles.
- How precise is the reported ratio?
- The calculator rounds the ratio to four decimal places, which is ample for most engineering, brewing, and laboratory work. Supply more precise density inputs if you need a tighter figure.