Specific Gravity to API Gravity Calculator

Calculator

Conversion direction * Specific Gravity → API Gravity API Gravity → Specific Gravity

Choose which value you want to calculate.

Specific gravity (SG) at temperature T *

Enter SG relative to water at the same reference.

API gravity *

Commonly used for petroleum liquids.

Reference temperature T *

Typical petroleum reference is 60°F.

Temperature unit °F °C

Used only for the optional correction.

Apply temperature correction to 60°F?

Yes, estimate SG at 60°F (SG60)

If unchecked, SG is treated as SG60.

Thermal coefficient α

Leave blank for 0 (no correction).

α unit per °F per °C

Converted internally to per °F.

Output precision API: 4 decimals API: 3 decimals API: 2 decimals

This changes on-screen formatting only.

Calculate Reset

Example data table

Values assume SG at 60°F with no correction.

Formula used

• API gravity from SG60: API = (141.5 / SG60) − 131.5
• SG60 from API gravity: SG60 = 141.5 / (API + 131.5)
• Optional correction (simple estimate): SG60 ≈ SG_T × (1 + α × (T − 60°F))

The correction is an approximation and depends on the fluid’s thermal behavior. For compliance work, follow your industry standard method.

How to use this calculator

1. Select the conversion direction you need.
2. Enter SG or API gravity, depending on your choice.
3. Keep T at 60°F if you already have SG60.
4. Enable correction only when your value is at T.
5. Provide α if you have a suitable coefficient.
6. Press Calculate to view results above the form.
7. Use CSV or PDF to export the computed summary.

Article: Specific gravity to API gravity

1) What the numbers represent

Specific gravity (SG) compares a liquid’s density to water at a reference temperature, commonly 60°F. API gravity is a petroleum scale that expresses the same idea in a spread-out range. Higher API means a lighter liquid; lower API means a heavier liquid.

2) The core conversion

The relationship is direct: API = (141.5 / SG60) − 131.5. The reverse is SG60 = 141.5 / (API + 131.5). Because it is a transform, small SG changes near 1.00 can shift API noticeably. Enter SG with enough precision (for example 0.8450 instead of 0.85) for better results.

3) Temperature and reference conditions

Density changes with temperature. If your SG is already referenced to 60°F (SG60), you can convert immediately. If your SG was measured at another temperature, correct it to an equivalent SG60 first. This calculator includes an optional linear correction using a coefficient α, which should be treated as an estimate unless you have product-specific data.

4) Typical ranges in practice

Many crude oils fall roughly between 10 and 45 API. Refined products such as gasoline tend to be higher, while heavier residuals are lower. As a quick check, an SG around 0.85 often lands in the mid‑30s API, and an SG around 0.95 trends toward the mid‑teens. If your result is far outside these bands, re-check temperature and decimal places.

5) Why API gravity is used

API gravity is used for pricing language, blending targets, storage planning, and reporting. It can also support process expectations, because lighter feedstocks usually yield more low-boiling fractions.

6) Common input mistakes

Mixing reference temperatures is the most frequent error. Another is entering an impossible SG (zero or negative). Also remember: water near SG 1.000 corresponds to about 10 API. Values far outside typical ranges should be rechecked before sharing or exporting.

7) Interpreting results responsibly

For engineering and documentation, the converted value is a useful descriptor, but it does not replace a certified lab report. If the number will be used for custody transfer or compliance, follow the relevant standards and procedures.

8) Practical workflow

Confirm whether your SG is at 60°F. If not, apply a correction or use authoritative tables, then convert to API. Export the summary to CSV or PDF so assumptions (temperature, coefficient, and inputs) stay attached for later review.