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35.0 °API
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Calculator inputs
Choose a conversion, enter one value, set precision, and calculate. Density relationships use the selected reference-water density.
Batch conversion and CSV tools
Paste values separated by commas, spaces, semicolons, or new lines. Batch mode supports SG-to-API and API-to-SG calculations.
Saved calculation history
History is stored only in this browser. No calculation data is sent elsewhere.
Illustrative petroleum product presets
These broad values are examples, not certificates of product quality. Actual density varies by grade, blend, temperature, and specification.
| Material example | Illustrative SG | Approximate API | Use preset |
|---|---|---|---|
| Gasoline-range liquid | 0.740 | 59.72 °API | |
| Kerosene-range liquid | 0.810 | 43.19 °API | |
| Diesel-range liquid | 0.840 | 36.95 °API | |
| Light crude example | 0.830 | 38.98 °API | |
| Medium crude example | 0.880 | 29.30 °API | |
| Heavy crude example | 0.950 | 17.45 °API | |
| Extra-heavy example | 1.020 | 7.23 °API |
Interactive API versus specific-gravity chart
Move the pointer across the curve to inspect approximate values. The nonlinear relationship means equal SG changes do not produce equal API changes.
Chart range: SG 0.55 to 1.20.
Quick reference table
Values use the standard 60°F reference and 999.016 kg/m³ reference-water density.
| Specific gravity | API gravity | Approx. density | Classification | Relative to water |
|---|---|---|---|---|
| 0.600 | 104.333 °API | 599.41 kg/m³ | Light crude oil | Lighter than water |
| 0.650 | 86.192 °API | 649.36 kg/m³ | Light crude oil | Lighter than water |
| 0.700 | 70.643 °API | 699.31 kg/m³ | Light crude oil | Lighter than water |
| 0.750 | 57.167 °API | 749.26 kg/m³ | Light crude oil | Lighter than water |
| 0.800 | 45.375 °API | 799.21 kg/m³ | Light crude oil | Lighter than water |
| 0.825 | 40.015 °API | 824.19 kg/m³ | Light crude oil | Lighter than water |
| 0.850 | 34.971 °API | 849.16 kg/m³ | Light crude oil | Lighter than water |
| 0.875 | 30.214 °API | 874.14 kg/m³ | Medium crude oil | Lighter than water |
| 0.900 | 25.722 °API | 899.11 kg/m³ | Medium crude oil | Lighter than water |
| 0.950 | 17.447 °API | 949.07 kg/m³ | Heavy crude oil | Lighter than water |
| 1.000 | 10.000 °API | 999.02 kg/m³ | Extra-heavy crude oil | Approximately the same density as water |
| 1.050 | 3.262 °API | 1,048.97 kg/m³ | Extra-heavy crude oil | Heavier than water |
| 1.100 | -2.864 °API | 1,098.92 kg/m³ | Extra-heavy crude oil | Heavier than water |
Formula used
Specific gravity to API gravity
API gravity = (141.5 ÷ specific gravity) − 131.5
Example using SG 0.85:
API = (141.5 ÷ 0.85) − 131.5 = 34.9706°API
API gravity to specific gravity
Specific gravity = 141.5 ÷ (API gravity + 131.5)
Example using 35°API:
SG = 141.5 ÷ (35 + 131.5) = 0.84985
Density relationship
Density = specific gravity × reference-water density
At the standard reference used here, water density is approximately 999.016 kg/m³. Exact professional calculations may use approved tables and observed-to-standard temperature corrections.
How to use this calculator
- Select the conversion direction that matches your known value and desired result.
- Enter specific gravity, API gravity, or density in the main value field.
- Choose a density unit whenever density is an input or output.
- Keep the standard 60°F reference for conventional petroleum API calculations.
- Select precision, rounding behavior, notation, and trailing-zero preferences.
- Review the instant preview, then submit for a server-generated result and printable report.
- Use batch conversion when comparing many samples, then export the results as CSV.
Understanding specific gravity and API gravity
Specific gravity is a dimensionless ratio comparing a liquid’s density with the density of water at stated reference conditions. A specific gravity below one generally describes a liquid that is less dense than water, while a value above one describes a liquid that is denser. The number has no unit because both densities use the same unit and cancel during division. Temperature matters because liquids expand or contract as temperature changes. A density measurement without a reference temperature can therefore be misleading.
API gravity is an industry scale developed for petroleum liquids. It transforms specific gravity into a number that increases as petroleum becomes lighter. This direction can seem unusual at first: a low specific gravity produces a high API gravity, and a high specific gravity produces a low API gravity. The scale is convenient for comparing crude oils, refinery streams, fuels, and other hydrocarbon liquids. API gravity is written in degrees API, although it is not an angular measurement.
Why the 60°F reference matters
The familiar constants 141.5 and 131.5 are used with specific gravity referenced to 60°F. A laboratory hydrometer reading observed at another temperature may require correction before applying the formula. This page lets you explore a custom reference-water density for educational comparisons, but that option does not replace recognized petroleum measurement procedures. Commercial transactions, custody transfer, inventory control, and regulated reporting commonly demand calibrated instruments, certified temperature readings, approved tables, and documented correction methods.
Interpreting crude-oil categories
Common descriptive boundaries classify oils above 31.1°API as light, from 22.3°API through 31.1°API as medium, above 10°API but below 22.3°API as heavy, and at or below 10°API as extra-heavy. These labels provide a quick density-based description. They do not fully predict sulfur content, viscosity, acidity, contaminant levels, refining yield, market value, or production difficulty. Two oils with similar API gravity can behave differently because their chemical compositions differ.
Density conversions and limitations
The density tools first normalize values to kilograms per cubic metre. They then calculate specific gravity using the selected reference-water density. Conversions among kilograms per cubic metre, grams per cubic centimetre, pounds per cubic foot, and pounds per US gallon use fixed unit factors. Rounding is applied only for display; the internal calculation retains greater precision. Very small, very large, negative, or otherwise unusual results trigger warnings so users can check their source data.
Practical uses
Engineers and operators use API gravity to compare feedstocks, estimate handling behavior, review blending targets, communicate crude grades, and perform preliminary material balances. Students use the relationship to understand density ratios and reciprocal formulas. Buyers and sellers may see API gravity in product specifications, but contractual values should come from accepted test methods rather than a general web calculator. This tool is best for learning, estimation, checking arithmetic, and preparing noncritical comparisons.
Frequently asked questions
What does 10°API mean?
At the standard reference, 10°API corresponds to a specific gravity of 1.0. A petroleum liquid above 10°API is generally less dense than water, while one below 10°API is generally denser.
Can API gravity be negative?
Yes. A sufficiently dense liquid can produce a negative API value. However, API gravity at or below −131.5 cannot be inverted with the standard equation because the denominator would be zero or negative.
Why does higher API gravity mean lighter oil?
The formula contains specific gravity in the denominator. As specific gravity decreases, the quotient increases, so the API value rises.
Is specific gravity exactly equal to density in g/cm³?
They are often numerically close near ordinary reference temperatures because water density is near 1 g/cm³. They are not conceptually identical: specific gravity is a ratio and has no unit.
Can this calculator replace laboratory testing?
No. It converts supplied values and provides educational estimates. Laboratory testing determines the source density or specific gravity under controlled, documented conditions.
Important measurement disclaimer
This calculator is intended for education, estimation, and arithmetic checking. The standard formula assumes specific gravity at 60°F. Laboratory, refinery, shipping, fiscal, custody-transfer, and safety decisions may require calibrated equipment, certified sampling, temperature and pressure corrections, approved petroleum tables, and applicable industry or regulatory procedures. Do not use an unverified calculator result as the sole basis for commercial settlement, equipment design, hazardous-material handling, or legal compliance.