API Gravity Blend
Predicts the API gravity you get when two crude streams share one tank. Gravity does not blend linearly in API degrees — this tool converts each stream to specific gravity, weights by volume fraction, and converts back, the way a terminal operator or scheduler checks a blend before committing it to a railcar or pipeline batch.
Enter each stream's API gravity and its volume (any consistent unit) — the blended gravity updates live.
All results are an engineering estimate — not for custody transfer. Field measurement and certified tables govern.
Why API degrees are not averaged directly
The calculator converts each API gravity to specific gravity using SG = 141.5 ÷ (API + 131.5). It then weights each specific gravity by its fraction of the combined volume. Finally, API = 141.5 ÷ SG − 131.5 converts the estimated blend back to API degrees.
Worked example
As a hypothetical example, equal volumes of a 30° API stream and a 40° API stream produce an estimate of 34.85° API, rather than the simple average of 35°. Both inputs must use the same volume unit and a consistent reference basis.
Assumptions to check
This model assumes additive volumes and comparable reference conditions. It does not model shrinkage, temperature changes, or chemical compatibility. A predicted gravity does not establish a product specification or authorize a transfer. Confirm actual blend properties through the applicable measurement process.
Related tools and next steps
Explore the API gravity converter or BS&W net volume calculator. For operating support, see our terminal services.