Specific Gravity Calculator - SG = ρ Substance ÷ ρ Water

Substance Density

0.0125,000

Reference Density

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.

Why Use a Specific Gravity Calculator?

Specific gravity is simple division, but having a dedicated calculator avoids unit-conversion mistakes (mixing kg/m³, g/cm³, and g/mL) that are common when comparing densities from different sources or instruments.

The result updates live as you adjust either density value, and the step-by-step breakdown includes a plain-language interpretation (denser, less dense, or equal to the reference) so you don't have to remember which direction the ratio implies floating or sinking.

Because specific gravity is unitless, it's directly comparable across different measurement systems, useful when combining lab data reported in different units.

Who Should Use This Calculator?

Chemistry and physics students verifying homework problems involving density ratios and material identification.

Geologists and mineralogists comparing measured mineral densities against reference values to help identify unknown samples.

Brewers and winemakers tracking sugar content and fermentation progress via specific gravity readings from hydrometers.

Quality control technicians checking battery acid, fuel, or oil density against expected specification values.

Construction and materials engineers evaluating aggregate and soil density properties relative to water.

What Insights Does This Calculator Give You?

Specific gravity, the primary result, a unitless number showing how many times denser (or less dense) the substance is compared to the reference.

Density difference, the raw gap between the substance and reference densities, useful for understanding the magnitude of the difference in the same units you entered.

Float-or-sink interpretation, the step-by-step breakdown tells you directly whether the substance would sink, float, or match the reference fluid's density.

How to use this Specific Gravity calculator

Enter the substance density, the density of the material you're evaluating, in kg/m³.
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).
Read the specific gravity result, the highlighted result shows the unitless SG ratio.
Check the step-by-step breakdown, expand the calculation steps to see the substitution and a plain-language float/sink interpretation.

Show formula & methodology ↓Show less ↑

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

What is the formula for specific gravity?

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.

Why is water used as the reference for specific gravity?

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.

What does a specific gravity greater than 1 mean?

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.

What does a specific gravity less than 1 mean?

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.

How is specific gravity different from density?

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.

Can specific gravity be used for gases?

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.

How is specific gravity used in industry?

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.

What instrument is used to measure specific gravity directly?

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).

Does temperature affect specific gravity readings?

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.

How do I find the specific gravity of an unknown mineral or gemstone?

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.

What is the specific gravity of common everyday liquids?

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.

How does specific gravity relate to buoyancy?

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