Specific Gravity Calculator
Density as a ratio, plus the API petroleum scale.
Work out Specific Gravity. Density as a ratio, plus the API petroleum scale. Says where the formula stops holding.
Water at 4 °C is 1000. Use 1.225 to compare gases against air.
Specific gravity
0.789
Less dense than the reference — it floats
Specific gravity is density as a ratio, so it has no units and is the same number in every unit system — which is why it survives on hydrometers and in industry standards long after most ratios were replaced. Anything below 1.0 floats in water. The API scale used for crude oil runs backwards on purpose: lighter, more valuable oil scores higher, so 40° API is a better barrel than 20°.
How the Specific Gravity Calculator works
Enter a density and a reference to get specific gravity, whether it floats, and the API gravity used in the oil industry. Because it is a ratio it carries no units, which is why it survives on hydrometers and in standards.
Also known as: relative density calculator · api gravity calculator · density to specific gravity converter · will it float in water
Frequently asked questions
What is specific gravity?
The ratio of a substance's density to a reference, usually water at 4 °C. It is dimensionless, so the number is the same in every unit system.
How is it different from density?
Only in that it is a ratio. A density of 789 kg/m³ is a specific gravity of 0.789 against water — same information, no units attached.
What does specific gravity tell me about floating?
Anything below 1.0 floats in water and anything above sinks. It also gives the fraction submerged directly: 0.8 means 80% of the object sits below the waterline.
Why does the API scale run backwards?
Deliberately. API gravity = 141.5/SG − 131.5, so lighter and more valuable crude scores higher. A 40° API barrel is worth more than a 20° one, and the scale was built to reflect that.
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