API Gravity Calculator
Enter oil specific gravity or the required density relationship. The calculator returns API gravity in degrees API.
Calculation context and source notes
API gravity converts oil specific gravity into the API gravity scale used to classify crude oil density in petroleum engineering workflows.
Use it for PVT screening, crude-oil density checks, and empirical oil correlations that require API gravity. Confirm that the specific gravity is referenced to the standard temperature basis expected by the correlation.
Solves for
API (dimensionless)
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Formula, variables, and sourceRelated source-backed guides
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns API = 34.970588 dimensionless. Defaults demonstrate the implementation; they are not recommended field values.
0.85
Input definitions
SG_o
dimensionlessSpecific Gravity of Oil Phase
Output definitions
API
API Gravity
SG_o
Specific Gravity of Oil Phase (rearranged)
Engineering use, assumptions, and limits
Use it for PVT screening, crude-oil density checks, and empirical oil correlations that require API gravity. Confirm that the specific gravity is referenced to the standard temperature basis expected by the correlation.
Assumptions
- Specific gravity is referenced to the same standard conditions required by the equation.
- The oil sample density is representative of the fluid being evaluated.
- Inputs are not mixed between density, relative density, and API gravity forms.
Limitations
- API gravity is a density index, not a complete crude assay.
- Does not describe viscosity, composition, sulfur content, wax, asphaltenes, or phase behavior.
Common mistakes
- Using water density at nonstandard conditions without correction.
- Treating API gravity as a direct measure of oil quality for every engineering purpose.
- Entering API gravity where a correlation expects specific gravity.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
U.S. Bureau of Mines. (1921). Definition and calculation of API gravity.
Open source reference