How this calculator works
API gravity is an inverse density scale for petroleum. A larger API value means a smaller specific gravity. Both the oil and reference water densities must correspond to 60 F for the usual 60/60 F definition. The adjustable water density makes the conversion convention visible. Product names such as diesel or gasoline cover broad composition-dependent ranges, so use a measured density instead of assigning a fixed product value. This page does not correct a measurement taken at another temperature.
Formula
API = 141.5/SG - 131.5; SG = 141.5/(API + 131.5); rho = SG rho_water. SG is dimensionless and API is a conventional scale, not an angle.
Worked example
Specific gravity 0.8 gives 45.375 degrees API. Specific gravity 1 gives 10 degrees API. With the rounded reference density 999 kg/m3, SG 0.8 corresponds to 799.2 kg/m3.
Advertisement
Frequently asked questions
Is a larger API value a heavier oil?
No. API increases as specific gravity decreases, so a larger value describes a lighter petroleum liquid.
Can I enter a density measured at 20 C?
First correct it to 60 F using the appropriate petroleum temperature-correction method. The calculator itself makes no temperature correction.
Why is water 10 degrees API?
Putting SG = 1 into the definition gives 141.5 - 131.5 = 10.