Density from Specific Gravity: Formula and Examples

This calculator finds density from specific gravity (also called relative density) and a reference-fluid density. Enter specific gravity and the reference density; it returns the material’s density in the same density units. For liquids and solids, water is a common reference, but the reference must match the specific-gravity value’s definition.

Formula

Density = specific gravity × reference density, or ρ = SG × ρ_ref.

• ρ is the material’s density, here in kilograms per cubic metre (kg/m³).
• SG is specific gravity, a ratio with no units.
• ρ_ref is the reference substance’s density, entered here in kg/m³.

The calculator uses the entered reference density directly. Specific gravity is defined as the material density divided by the reference density, so rearranging that definition gives the formula above. If the reference density is entered in another unit, convert it first or use a calculator configured for that unit; the calculated density has the same unit as the reference density.

Worked Example

Using the calculator’s defaults, specific gravity is 1.2 and reference density is 1000 kg/m³.

1. Write the relationship: ρ = SG × ρ_ref.
2. Substitute the values: ρ = 1.2 × 1000 kg/m³.
3. Multiply: ρ = 1200 kg/m³, or 1200.00 kg/m³ to the calculator’s two decimal places.

The result means the material has 1.2 times the density of the specified reference under the conditions used to define its specific gravity.

What Specific Gravity Means

Density is mass per unit volume, such as kilograms per cubic metre or grams per millilitre. Specific gravity compares one density with another. Because both densities use the same units, those units cancel, leaving a dimensionless number.

A specific gravity of 1 means equal density to the reference substance. A value above 1 means denser than the reference; a value below 1 means less dense. These comparisons do not by themselves describe every material’s behavior: buoyancy also depends on the fluid surrounding an object, and solids may have pores or trap air.

For many ordinary liquid and solid measurements, water is used as the reference. However, water density changes slightly with temperature, and a specific-gravity measurement may specify a temperature for both the sample and reference. Gas specific gravity is often defined relative to air instead. Always check the measurement’s stated convention rather than assuming every reported value uses water.

Using the Calculator and Choosing a Reference

Enter the specific-gravity value as a plain ratio, not as a percentage. Enter the density of the correct reference substance in the unit you want for the answer. The output uses that same density unit.

• For a water-referenced liquid or solid, use the water density appropriate to the stated temperature and measurement convention when precision matters. Around room temperature, water is close to 1000 kg/m³, which is convenient for an estimate, not an exact value for every temperature.
• For a gas value referenced to air, enter air density under the relevant conditions, not water density.
• For US customary results, use a reference density in units such as lb/ft³; the resulting density will also be in lb/ft³. Do not multiply a dimensionless specific gravity by a number in incompatible units.

Specific gravity does not determine a density on its own unless the reference substance and its density are known. If a value is given only as “SG = 0.8,” for example, you still need to know what reference and conditions the source intended.

When the Calculation Is Useful

This conversion is useful when a material specification, hydrometer reading, or reference table gives specific gravity but a calculation requires density. Once density is known, it can be used with volume to calculate mass: mass = density × volume. Keep the volume unit consistent with the density unit—for example, kg/m³ pairs directly with m³ to give kilograms.

For an illustrative water-referenced value of SG = 0.8, using 1000 kg/m³ as an approximate reference gives 0.8 × 1000 = 800 kg/m³. If the reference density or temperature differs, the result changes proportionally. This is why reference conditions matter, especially when comparing measurements or working to more than a rough estimate.

Common Mistakes and Limits

• Using the wrong reference: A value relative to air cannot be converted using water density. Confirm the stated reference first.
• Mixing units: Specific gravity has no units, but the reference density does. The answer inherits the reference density’s units.
• Treating SG as a percentage: Enter 1.2 for a ratio of 1.2, not 120, and do not add a percent sign unless the source explicitly presents a percentage that needs conversion.
• Ignoring temperature: Density depends on temperature, and specific-gravity conventions may identify measurement temperatures. A rounded water density is not suitable for every precision task.
• Overinterpreting the result: The calculation converts a ratio into density; it does not correct a faulty measurement, identify a material, or account for bubbles, contamination, or changes in composition.

The calculator displays two decimal places, but that formatting does not make the input more precise. The meaningful precision is limited by the accuracy of the specific-gravity reading and reference density. For laboratory or engineering work, use the specified conditions and precision requirements of the measurement method.

Frequently Asked Questions

How do you calculate density from specific gravity?
Multiply specific gravity by the density of its reference substance: density = SG × reference density. The result has the same units as the reference density.

Is specific gravity the same as density?
No. Density is mass per volume and has units. Specific gravity is a unitless ratio comparing a material’s density with a reference density.

What is the density if specific gravity is 1?
It equals the density of the stated reference substance under the relevant conditions. If the reference is water approximated as 1000 kg/m³, the estimate is 1000 kg/m³.

Can specific gravity be less than 1?
Yes. It means the material is less dense than its reference substance. For a water-referenced liquid, an SG below 1 indicates lower density than the chosen water reference.

Does specific gravity change with temperature?
It can, because the densities of the sample and reference can change with temperature. Check the measurement’s temperature convention when precision or comparisons matter.

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in sg | Specific gravity | - | 1.2 | 0
in ref | Reference density | kg/m^3 | 1000 | 0
out dens | Density | kg/m^3 | sg * ref | 2