Petroleum unit converter
Twenty-one families of upstream units, converted in one place — including the awkward ones like bbl/ft, psi/ft and millidarcy.
Units & conversion
API gravity, density & temperature correction
°API, specific gravity and density at 15 °C from a density observed at any temperature, with the volume correction factor that gets you there.
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How it is calculated
- Thermal expansion coefficient α₆₀ = K₀/ρ₁₅² + K₁/ρ₁₅ + K₂, with the K constants taken from the commodity band you select (54A crude, 54B products, 54D lubricating oils).
- VCF = exp[−α₆₀·ΔT·(1 + 0.8·α₆₀·ΔT)], with ΔT measured from the 15 °C basis.
- α depends on ρ₁₅, which is what is being solved for, so ρ₁₅ is found by fixed-point iteration rather than one pass.
- °API = 141.5/SG₆₀₆₀ − 131.5, with SG referenced to water at 60 °F (999.016 kg/m³).
Standards it speaks
Where this stops being true
This is the D1250-80 closed-form VCF, not the full API MPMS 11.1 (2004) implementation procedure. The 2004 standard specifies rounding at defined points and an explicit hydrometer correction; a custody ticket computed here and one computed by a certified meter can differ in the fourth significant figure. Use it to check a number, not to issue one.
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