API Gravity Calculator
Convert between API gravity and specific gravity to classify petroleum products per American Petroleum Institute standards.
Input
Enter either value — the other is calculated automatically.
dimensionless
°API
Quick Examples
Enter a value above to see results
Specific Gravity
—
dimensionless
API Gravity
—
degrees API
Grade
—
—
Density Equivalents
Density (kg/m³ at 60°F)
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Density (lb/gal at 60°F)
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Density (lb/bbl at 60°F)
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API Formulas
SG → API gravity
°API = (141.5 ÷ SG) − 131.5
API gravity → SG
SG = 141.5 ÷ (°API + 131.5)
Crude Oil Classification
| Grade | API Gravity |
|---|---|
| Light crude | > 31.1° |
| Medium crude | 22.3° – 31.1° |
| Heavy crude | 10° – 22.3° |
| Extra-heavy crude | < 10° |
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Summary
Convert between API gravity and specific gravity to classify petroleum products per American Petroleum Institute standards.
How it works
- Enter a specific gravity value (dimensionless ratio relative to water at 60°F) or an API gravity value.
- The calculator applies the API formula: API = (141.5 / SG) − 131.5.
- To convert back, the inverse formula is used: SG = 141.5 / (API + 131.5).
- Results are rounded to two decimal places for practical field use.
- The petroleum grade classification (light, medium, heavy, extra-heavy crude) is determined from the computed API gravity.
Use cases
- Determining crude oil grade before purchase or refining decisions.
- Converting laboratory specific gravity readings to API gravity for reporting.
- Classifying petroleum products (gasoline, diesel, kerosene, fuel oil) by API gravity.
- Checking whether a crude oil meets pipeline or refinery intake specifications.
- Educational use in petroleum engineering courses covering fluid properties.
- Field calculations when appraising oil wells or production streams.
Frequently Asked Questions
Last updated: 2026-07-01 ·
Reviewed by Nham Vu