API Gravity Calculator
Convert specific gravity (SG) to degrees API (°API) and back, classify crude oil as light, medium, heavy or extra-heavy, convert to kg/m³, lb/US gal and barrels per metric ton, and blend two crudes. The API scale is defined at 60°F.
Water at 60°F has SG = 1.000. Most traded crudes fall between 0.78 and 1.02.
Water = 10°API. Light crudes are above 31.1°API.
Common crude benchmarks
Typical °API values — they vary by batch and assay. Tap one to load it into the calculator.
Quick reference: °API to density
| °API | SG | kg/m³ | lb/US gal | bbl / MT | Class |
|---|---|---|---|---|---|
| 10° | 1.0000 | 999.0 | 8.337 | 6.30 | Heavy crude |
| 15° | 0.9659 | 964.9 | 8.053 | 6.52 | Heavy crude |
| 20° | 0.9340 | 933.1 | 7.787 | 6.74 | Heavy crude |
| 25° | 0.9042 | 903.3 | 7.538 | 6.96 | Medium crude |
| 30° | 0.8762 | 875.3 | 7.305 | 7.19 | Medium crude |
| 35° | 0.8498 | 849.0 | 7.085 | 7.41 | Light crude |
| 40° | 0.8251 | 824.3 | 6.879 | 7.63 | Light crude |
| 45° | 0.8017 | 800.9 | 6.684 | 7.85 | Light crude |
| 50° | 0.7796 | 778.8 | 6.500 | 8.08 | Light crude |
| 55° | 0.7587 | 758.0 | 6.326 | 8.30 | Light crude |
| 60° | 0.7389 | 738.2 | 6.160 | 8.52 | Light crude |
Computed from °API = 141.5/SG − 131.5 with water at 60°F = 999.016 kg/m³ (ASTM D1250). Tables using older constants may differ by about 0.1 kg/m³.
Honest notes (read before trusting the numbers)
Which nrtechstudio tool do you need?
API Gravity Calculator (this page): the petroleum-specific scale — SG ↔ °API, crude classification, benchmarks, blending.
For plain density unit conversion (kg/m³ ↔ lb/ft³ ↔ g/cm³ …), use our Density Unit Converter.
For solving density from mass and volume of objects, use our Volume to Density Calculator (3-way solver with material table).
Frequently asked questions
What is API gravity?
API gravity is the petroleum industry's scale for how light or heavy a crude oil or petroleum liquid is compared with water. It is defined from specific gravity at 60°F by the formula °API = (141.5 / SG) − 131.5, and reported in degrees (°API). The scale is inverted: a higher °API means a lighter oil. Pure water at 60°F measures exactly 10° API.
How do I calculate API gravity from specific gravity?
Divide 141.5 by the specific gravity (measured 60°F/60°F), then subtract 131.5. Example: SG 0.85 → 141.5 / 0.85 = 166.47, minus 131.5 = 34.97° API, which classifies as light crude.
How do I convert °API back to specific gravity?
Use SG = 141.5 / (°API + 131.5). Example: 35° API → 141.5 / 166.5 = 0.8498. From SG you can also recover density: multiply by 999.016 kg/m³ (the density of water at 60°F), so 35° API ≈ 849.0 kg/m³.
What are the light, medium, heavy and extra-heavy cutoffs?
The commonly used convention (EIA/USGS) is: light crude above 31.1° API, medium crude from 22.3 to 31.1° API, heavy crude from 10 to 22.3° API, and extra-heavy oil below 10° API (denser than water). Treat these as industry convention, not a legal definition — agencies and contracts sometimes draw the lines slightly differently.
At what temperature is API gravity defined?
At 60°F (15.6°C), with specific gravity referenced 60/60°F. Oil expands when warm, so the same oil reads a higher °API when hot and a lower °API when cold. Correcting a field measurement to 60°F requires the ASTM D1250 petroleum measurement tables. This calculator does not perform temperature correction — enter values already corrected to 60°F.
Why can't I just average °API values when blending crudes?
Because °API is nonlinear in density, averaging the degrees gives the wrong answer. The correct method is to convert each crude to SG, take the volume-weighted average SG, and convert back. Example: 50 barrels of WTI at 39.6° API (SG 0.8270) plus 50 barrels of Maya at 22.08° API (SG 0.9213) gives SG (0.8270 + 0.9213) / 2 = 0.8742, which is 30.37° API (medium) — not the naive average of 30.84°. The Blend tab on this page does this math for you.
How do I convert °API to kg/m³?
First compute SG = 141.5 / (°API + 131.5), then multiply by 999.016 kg/m³, the ASTM D1250 density of water at 60°F. Example: 35° API → SG 0.8498 → 849.0 kg/m³. Reference tables built on older water-density constants may differ by about 0.1 kg/m³.
How do I convert °API to lb per US gallon?
Convert to kg/m³ as above, then multiply by 0.0083454 (exactly 2.2046226218 lb/kg divided by 264.17205236 gal/m³). Example: SG 0.85 → 849.2 kg/m³ → 7.087 lb/gal.
How many barrels per metric ton is a given °API?
Use bbl/MT = 1000 / (density in kg/m³ × 0.1589873 m³/bbl). Example: WTI at 39.6° API (826.2 kg/m³) ≈ 7.61 barrels per metric ton. Cargo and trading desks use this to convert between volume and mass.
Can API gravity be below 10 or above 60?
Yes. Below 10° API means denser than water — for example Athabasca bitumen at about 8° API. Above 60° covers very light condensates. The scale has no hard upper bound, though values far outside roughly 5–70 are rare among traded crudes.
Does a higher °API always mean a more valuable crude?
Generally yes: lighter crudes yield more gasoline and diesel per barrel and usually trade at higher prices. But it is not a guarantee — refinery configuration, sulfur content, and location also set the price, and some very light condensates above about 45° API are actually discounted because their molecules are too short for standard refineries.
How is this different from a density unit converter?
A density converter only changes units, for example kg/m³ to lb/ft³. This tool implements the petroleum-specific API scale: two-way SG to °API conversion, crude classification, benchmark crudes, blending math, and petroleum density readouts. For plain density unit conversion, use our Density Unit Converter.
Free tool by NRTechStudio