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Specific Gravity Calculator

Physics

Calculate specific gravity by dividing a substance's density by a reference density (water by default). Instant unitless SG ratio with formula steps.

0.0125,000
0.0125,000

Specific Gravity

2.7
Density Difference
1,700

This calculator computes your Specific Gravity, Density Difference from the values you enter.

Inputs
Substance DensityReference Density
Outputs
Specific GravityDensity Difference

What is a Specific Gravity?

The Specific Gravity Calculator computes the unitless ratio between a substance's density and a reference density (water at 1,000 kg/m³ by default), using SG = ρ(substance) ÷ ρ(reference). Enter the substance's density and the reference density, and the calculator instantly returns the specific gravity along with the raw density difference.

Specific gravity is a widely used way to describe how dense a material is relative to a well-known standard, making density comparisons intuitive across chemistry, geology, brewing, and engineering. If you need to compute density itself from mass and volume first, use the Density Calculator.

How to use this Specific Gravity calculator

  1. Enter the substance density — the density of the material you're evaluating, in kg/m³.

  2. Enter the reference density — defaults to 1,000 kg/m³ for water; change this if comparing against a different reference fluid (like air for gas density comparisons).

  3. Read the specific gravity result — the highlighted result shows the unitless SG ratio.

  4. Check the step-by-step breakdown — expand the calculation steps to see the substitution and a plain-language float/sink interpretation.

Formula & Methodology

Specific gravity formula:
SG = ρ(substance) ÷ ρ(reference)

Variable definitions:
- ρ(substance) — density of the substance being measured (kg/m³)
- ρ(reference) — density of the reference substance, typically water at 1,000 kg/m³
- SG — specific gravity (unitless)

Worked example:

Aluminum has a density of 2,700 kg/m³, compared against water at 1,000 kg/m³.

SG = 2,700 ÷ 1,000 = 2.7

This means aluminum is 2.7 times denser than water, and would sink if placed in it.

Note: For precise scientific or industrial use, specific gravity should be reported alongside the measurement temperature, since density (and therefore SG) can shift slightly with temperature for both the substance and the reference fluid.

Frequently Asked Questions

Specific gravity (SG) is calculated as SG = ρ(substance) ÷ ρ(reference), where both densities are in the same units. The result is a unitless ratio, since the units cancel out — it simply describes how many times denser (or less dense) a substance is compared to the reference, typically water.
Water at 4°C has a density of almost exactly 1,000 kg/m³ (1 g/cm³), making it a convenient, universally recognized reference point for solids and liquids. A specific gravity of 2 means a substance is twice as dense as water, while 0.5 means half as dense.
A specific gravity greater than 1 means the substance is denser than the reference (usually water), so it will sink if placed in that reference fluid. Most metals (iron SG ≈ 7.87, aluminum SG ≈ 2.7) have specific gravity well above 1.
A specific gravity less than 1 means the substance is less dense than the reference, so it will float. Ice (SG ≈ 0.92), most oils (SG ≈ 0.8–0.95), and cork (SG ≈ 0.24) all have specific gravity below 1, which is why they float on water.
Density is a dimensional quantity (like kg/m³ or g/cm³) describing mass per unit volume, while specific gravity is a unitless ratio comparing that density to a reference substance's density. Use the [Density Calculator](/density-calculator/) to compute density directly from mass and volume first, then use this calculator to convert it to specific gravity.
Yes — for gases, specific gravity is usually calculated relative to dry air (about 1.225 kg/m³ at sea level) instead of water, describing whether a gas is heavier or lighter than air. Natural gas, for example, has a specific gravity of about 0.6 relative to air, meaning it's lighter and rises.
Specific gravity is widely used to test battery acid concentration, measure sugar content in brewing and winemaking (via hydrometers), verify fuel and oil quality, assess soil and aggregate properties in construction, and identify minerals and gemstones by comparing measured SG to known reference values.
A hydrometer is the most common instrument for measuring the specific gravity of liquids directly — it floats at a depth proportional to the liquid's density, with a calibrated scale read at the liquid's surface. For solids, specific gravity is typically measured using Archimedes' principle (comparing weight in air versus weight submerged in water).
Yes — because most substances (including the reference water) expand and change density with temperature, specific gravity should ideally be reported alongside the measurement temperature (e.g., "SG at 20°C") for precision, since a substance's SG relative to water can shift slightly at different temperatures.
Measure the mineral's mass in air, then its apparent mass while fully submerged in water; the difference gives the buoyant force, which relates to the volume of water displaced. Divide the mineral's density (mass ÷ displaced volume) by water's density (1,000 kg/m³) using this calculator to get its specific gravity, then compare against reference tables to help identify the mineral.
Milk has an SG of about 1.03, olive oil about 0.91, honey about 1.42, and seawater about 1.025 — all measurable relative to plain water using this calculator by entering each liquid's density.
An object floats in a fluid if its specific gravity (relative to that fluid) is less than 1, and sinks if it's greater than 1 — this is a direct consequence of Archimedes' principle. Specific gravity is therefore a quick way to predict floating or sinking behavior without doing a full buoyancy force calculation.
Also known as
SG calculatorrelative density calculatordensity ratio calculatorspecific gravity formula calculator