Formula used
Step 1: Convert API gravity to specific gravity at 60°F: SG = 141.5 / (API + 131.5)
Step 2: Convert specific gravity to density at the reference temperature: ρref = SG × ρwater (default ρwater = 999.016 kg/m³ at 60°F).
Optional: Apply a simple linear temperature correction (quick estimate): ρ(T) = ρref / (1 + α·ΔT) where ΔT is in °C.
How to use this calculator
- Enter the API gravity value in °API.
- Select your preferred output unit for density.
- Keep water density at default, or adjust if required.
- If needed, enable temperature correction and set temperatures.
- Enter α for your fluid, then click Calculate.
- Use Download CSV or Download PDF to export results.
Example data table
| API (°API) | SG @ 60°F | Density @ 60°F (kg/m³) | Density @ 60°F (lb/ft³) |
|---|---|---|---|
| 10.00 | 1.000000 | 999.016 | 62.367 |
| 20.00 | 0.933993 | 933.074 | 58.250 |
| 30.00 | 0.876161 | 875.299 | 54.643 |
| 40.00 | 0.825073 | 824.261 | 51.457 |
API gravity and density guide
1) What API gravity tells you
API gravity is a petroleum-industry scale that compares a fluid’s density to water at a reference condition. Higher °API means a lighter fluid, and lower °API means a heavier fluid. For many crudes, values commonly sit around 10–45 °API, while refined products often trend higher.
2) Converting API to specific gravity
The calculator first converts °API to specific gravity at 60°F using SG = 141.5/(API + 131.5). This step is dimensionless and is useful because it normalizes different fluids against water. For example, 35 °API gives an SG close to 0.85, indicating it is lighter than water.
3) Density at the reference temperature
Once SG is known, reference density is found by multiplying by a chosen water density constant. The default 999.016 kg/m³ is a practical reference near 60°F. Using the same constant across comparisons improves consistency, especially when building property tables or checking tank gauging results.
4) Why temperature matters
Liquids expand as temperature rises, so density usually decreases as temperature increases. Even a modest change can matter in custody transfer, blending, and mass-balance checks. This calculator includes an optional linear correction to estimate density at a different temperature when you only have an API value and a typical expansion coefficient.
5) Choosing an expansion coefficient
The coefficient α is entered in 1/°C and represents how strongly volume changes with temperature. Many petroleum liquids fall roughly in the 0.0005–0.0010 range, but composition matters. If you have a lab sheet or product spec, use that value for improved accuracy.
6) Useful unit outputs
Engineering teams often need density in kg/m³ for calculations, while operations may prefer lb/ft³ or lb/US gal. The tool computes density in kg/m³ first, then converts, helping you avoid rounding mistakes. Use consistent units when comparing batches or supplier certificates.
7) Typical checks and sanity ranges
If your result seems unusual, do quick checks: higher °API must produce lower density, and heavy crudes (10–20 °API) generally yield densities above about 900 kg/m³ at reference conditions. Light products (40–60 °API) can drop closer to 750–830 kg/m³, depending on composition.
8) Best practices for reporting
Always report the reference condition, the water density constant used, and whether temperature correction was applied. If you used a generic α, label results as estimates. For audits and transfers, use standard tables when required by contract, and treat this calculator as a fast, transparent computation aid.
FAQs
1) What happens if I enter a very high API value?
High °API represents very light liquids, so the calculated density decreases. If you enter extremely high values, verify that the API number is correct and that you are not mixing product grades or reference conditions.
2) Is the temperature correction always accurate?
No. The linear correction is a quick estimate using α. Real fluids can deviate, and standard petroleum tables may be required for custody transfer. Use the correction for engineering approximations unless your process demands certified methods.
3) Why can I change the water density constant?
Different references and standards may use slightly different water density values. Keeping the constant explicit makes assumptions transparent. If your organization uses a specific value at a given reference temperature, enter it to match internal reporting.
4) What unit should I choose for pipelines and pumps?
Most hydraulic and pump power calculations use kg/m³ in SI or lb/ft³ in US customary systems. Choose the unit that matches your formulas and datasheets to avoid conversion errors during sizing and troubleshooting.
5) Does this calculator work for non-petroleum liquids?
API gravity is mainly used for petroleum liquids, but the math still converts an API value to an SG-like ratio. For chemicals, it is usually better to use direct specific gravity or density data at the needed temperature.
6) What does SG@60°F mean in the results?
It is the specific gravity computed from your API value at the reference condition. SG is dimensionless and compares the fluid to water. It is a convenient intermediate value before converting into density units.
7) How do I export results for a report?
After calculation, use the Download CSV button for spreadsheets or the Download PDF button for sharing. Both exports include the key inputs, the selected unit, and the computed density values for traceable documentation.