Specific Gravity Calculator

Related Calculators

Specific gravity: A unitless ratio that compares a substance's density to the chosen reference density [1].

Density: How much mass is packed into a certain volume, such as kg/m^3 or g/cm^3.

Reference density: The density used as the comparison baseline. This calculator defaults to water at 4 C.

Computed density in base SI: The intermediate density in kg/m^3 before any output-unit conversion.

Input unit set: The unit family that controls how "Substance density (selected unit)", "Mass (selected unit)", and "Volume (selected unit)" are interpreted.

Density comparison note: A short text result that tells you whether the substance is less dense than, about equal to, or denser than the reference fluid.

Mistake: Entering a value in "Substance density (selected unit)" while "What do you want to calculate?" is set to use "Specific gravity" or mass and volume.
Fix: Match the visible input to the selected mode. Use "Substance density (selected unit)" only when the mode is "Specific gravity from density".

Mistake: Typing mass in grams while "Input unit set" is set to kilograms and cubic meters.
Fix: Change "Input unit set" so it matches your actual measurements before reading "Density" or "Specific gravity".

Mistake: Using 0 or a negative number for "Volume (selected unit)" in the mass-volume mode.
Fix: Enter a volume greater than 0 so the calculator can compute "Computed density in base SI" and "Specific gravity" correctly.

Mistake: Treating "Specific gravity" like it has units such as kg/m^3 or g/cm^3.
Fix: Enter "Specific gravity" as a plain ratio with no unit, and read the actual unit-based result from "Density" instead.

Mistake: Forgetting that "Reference density" changes the ratio and then misreading the result.
Fix: Check "Reference density used" every time. If you chose "Custom reference density (kg/m^3)", make sure it is the exact comparison fluid you want.

Mistake: Choosing "Fixed decimals" but entering a non-whole or unrealistic "Decimal places" value.
Fix: Use a whole number for "Decimal places". Small values like 2, 3, or 4 usually make "Density" and "Specific gravity" easy to read.

• Specific gravity depends on the chosen baseline. If you change "Reference density", the ratio changes even when the material stays the same.
• The default reference is water at 4 C, using 999.972 kg/m^3 [2]. If your class, lab, or industry problem uses another temperature or another fluid, choose the matching reference.
• The calculator assumes consistent units within the selected "Input unit set". Wrong unit selection will give wrong density and specific gravity.
• Mass-volume mode assumes the sample has one average density over the measured volume. Mixed materials, trapped air, or measurement error can change real results.
• Negative density and negative specific gravity are treated as invalid here for ordinary physical materials, and volume must be greater than 0.
• The comparison note is only a density comparison. It is not a full float-or-sink prediction unless water is the reference, and even then shape and buoyancy details are not modeled.
• Rounded display settings can hide tiny differences, so use more decimals or scientific notation when values are very small or very large.

Core formulas

The calculator first converts inputs into consistent units, then applies the formula for the selected mode.

SG = ρ_substance / ρ_reference

ρ_substance = SG x ρ_reference

ρ_substance = m / V

SG = (m / V) / ρ_reference

How units are handled

Specific gravity has no unit because it is a ratio [1]. Density results are converted through base SI units, kg/m^3, so different input systems can be compared safely.

1 g/cm^3 = 1000 kg/m^3

1 lb/ft^3 = 16.018463 kg/m^3

1 lb/in^3 = 27679.90471 kg/m^3

When "Reference density" is set to water at 4 C, the calculator uses 999.972 kg/m^3 as the baseline [2]. If you choose a custom reference, that user-entered value becomes ρ_reference.

Worked mini-example

Suppose the mode is "Specific gravity from mass and volume" with mass 270 g, volume 100 cm^3, and water at 4 C as the reference.

ρ_substance = 270 / 100 = 2.7 g/cm^3

2.7 g/cm^3 x 1000 = 2700 kg/m^3

SG = 2700 / 999.972 = 2.700075604

That means the material is about 2.70 times as dense as the chosen reference fluid.

Interpretation logic

If the result is above 1, the substance is denser than the reference fluid. If it is below 1, it is less dense. If it is extremely close to 1 after calculation, the note says it is approximately equal to the reference fluid.

Calculation notes

In density-based mode, the entered "Substance density (selected unit)" is converted to kg/m^3 before computing specific gravity. In specific-gravity mode, the entered ratio is multiplied by the reference density to get the material density. In mass-volume mode, density is found from mass divided by volume first, then specific gravity is computed from that density. This follows the standard density-to-relative-density relationship used in measurement practice [3].

Assumptions used

The method assumes volume is greater than 0, reference density is greater than 0, and all visible inputs use the selected unit system consistently. It also assumes you want a density comparison, not a full fluid-mechanics model of buoyancy, temperature effects, or compressibility.