API Gravity Calculator

Category: Physics

- March 23, 2025

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Calculate API gravity, specific gravity, and density conversions for petroleum products. API gravity is a measure used by the petroleum industry to express the relative density of petroleum liquids.

Select Calculation Type

API Gravity from Specific Gravity

Specific Gravity from API Gravity

Density Conversion

Common Oil Types Reference

Select a common petroleum type:

Enter Specific Gravity

Specific Gravity at 60°F:

Advanced Options

Reference Temperature:

°C

Decimal Places:

About API Gravity

API gravity is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

Key Formulas

API Gravity from Specific Gravity: °API = (141.5 ÷ SG) - 131.5
Specific Gravity from API Gravity: SG = 141.5 ÷ (°API + 131.5)
Density (kg/m³) from Specific Gravity: ρ = SG × 999

Oil Classifications by API Gravity and Sulfur Content

Crude oils are commonly classified by both their API gravity (density) and sulfur content:

Light Sweet Crude: API gravity > 31.1°API with sulfur content < 0.5%. Examples: West Texas Intermediate (WTI) ~ 39-40°API, Brent Crude ~ 38°API, Nigerian Bonny Light ~ 35°API
Light Sour Crude: API gravity > 31.1°API with sulfur content > 0.5%. Examples: Russian Urals ~ 31-32°API with ~1.4% sulfur, Mars Blend ~ 28-30°API with ~1.8% sulfur
Medium Sweet Crude: API gravity between 22.3-31.1°API with sulfur content < 0.5%. Examples: Louisiana Sweet ~ 30°API
Medium Sour Crude: API gravity between 22.3-31.1°API with sulfur content > 0.5%. Examples: Arab Medium ~ 30°API with ~2.5% sulfur, Kuwait Export ~ 30°API with ~2.5% sulfur
Heavy Sweet Crude: API gravity < 22.3°API with sulfur content < 0.5%. Examples: Some Indonesian crudes
Heavy Sour Crude: API gravity < 22.3°API with sulfur content > 0.5%. Examples: Venezuelan Merey ~ 16°API with ~2.5% sulfur, Mexican Maya ~ 21°API with ~3.5% sulfur, Canadian oil sands ~ 8-12°API with ~4-5% sulfur
Extra Heavy Oil: API gravity < 10°API. Examples: Venezuelan Orinoco Belt crudes ~ 8-10°API, Canadian bitumen ~ 8°API

Typical API Gravity Ranges by Petroleum Product

Condensate: 50-80°API
Gasoline: 50-70°API
Kerosene/Jet Fuel: 40-50°API
Diesel/Heating Oil: 30-37°API
Light Lubricating Oils: 28-32°API
Heavy Lubricating Oils: 20-28°API
Fuel Oil: 12-20°API
Bunker Oil: 8-12°API
Asphalt: 5-10°API

Economic Importance of API Gravity

API gravity affects the economic value and processability of crude oils:

Refining: Light crudes are generally easier to refine and yield more high-value products like gasoline and diesel with less processing.
Pricing: Light crudes typically command price premiums over heavy crudes due to their superior yield of high-value products.
Sweet vs. Sour: Sweet crudes (low sulfur) are more valuable than sour crudes as they require less desulfurization, which is an expensive process.
Transportation: Heavy crudes may require diluents or heating for pipeline transportation, increasing logistics costs.

What Is the API Gravity Calculator?

The API Gravity Calculator is a tool that helps you convert between three related properties of petroleum liquids: API gravity, specific gravity, and density. These values are commonly used in the oil and gas industry to assess the quality and classification of crude oil and petroleum products.

API gravity, developed by the American Petroleum Institute (API), measures how heavy or light a petroleum liquid is compared to water. This tool makes it easy to switch between units, apply temperature correction if needed, and quickly determine classifications such as light or heavy crude oil.

Key Formulas Used

API Gravity from Specific Gravity:
°API = (141.5 ÷ SG) - 131.5

Specific Gravity from API Gravity:
SG = 141.5 ÷ (°API + 131.5)

Density from Specific Gravity:
ρ = SG × 999

Why Use This Calculator?

This calculator helps users make quick and accurate conversions based on standard industry formulas. It’s useful for:

Determining the quality and classification of petroleum liquids
Comparing product specifications in different units
Applying optional temperature correction for more precise results
Performing quick checks without needing to reference formulas or charts

How to Use the Calculator

Follow these steps to perform your desired calculation:

Select Calculation Type: Choose whether you want to calculate API gravity, specific gravity, or perform a density conversion.
Enter Input Value: Depending on the selected type, enter the specific gravity, API gravity, or density value.
Set Units: If you're using the density converter, choose your unit of measurement (e.g., kg/m³, lb/gal).
Optional Temperature Correction: You can enable this to correct for temperature-related density changes.
Click "Calculate": The tool will display results for API gravity, specific gravity, and density, along with step-by-step explanations.

Understanding the Results

The calculator provides three main outputs:

API Gravity: Indicates how heavy or light the liquid is. Higher values mean lighter oil.
Specific Gravity: The ratio of the liquid’s density to water at 60°F (15.6°C).
Density: The mass per unit volume, shown in your selected unit.

It also shows the classification based on API gravity:

Light Crude Oil: API gravity > 31.1°
Medium Crude Oil: 22.3° – 31.1°
Heavy Crude Oil: 10.0° – 22.3°
Extra Heavy Oil: API gravity < 10.0°

Frequently Asked Questions (FAQ)

What is API gravity?

API gravity is a measure of a petroleum liquid’s density relative to water. Values above 10 mean the liquid is lighter than water; values below 10 mean it is heavier.

What is specific gravity?

Specific gravity is the ratio of the liquid's density to the density of water at 60°F. It is a dimensionless number.

Why does temperature correction matter?

Temperature affects the density of liquids. As temperature increases, most petroleum liquids expand and become less dense. Temperature correction adjusts for this to provide a standardized comparison.

What units can I use for density?

The calculator supports common units such as:

kg/m³ (kilograms per cubic meter)
g/cm³ (grams per cubic centimeter)
lb/ft³ (pounds per cubic foot)
lb/gal (pounds per gallon)

Who is this tool useful for?

This calculator is helpful for professionals and students in the petroleum, chemical, and energy industries. It’s also handy for engineers, lab technicians, and anyone working with fuel and crude oil specifications.

Final Thoughts

Whether you're checking product specs, evaluating crude oil, or performing unit conversions, the API Gravity Calculator provides a fast and reliable way to get the numbers you need.