Observed → 60 °F · API MPMS Ch. 9.1 & 11.1
The temperature at which the hydrometer / densitometer reading was taken. The result is reduced to the 60 °F base.
How density and API gravity vary with temperature, and the MPMS 11.1 base-density iteration
Quick-reference chart of corrected API gravity at 60 °F for an observed hydrometer reading taken at the observed temperature, for generalized crude oil per API MPMS Chapter 11.1 / ASTM D1250. A reading above 60 °F corrects downward; below 60 °F, upward.
| Observed °API | 40 °F | 50 °F | 70 °F | 80 °F | 90 °F | 100 °F |
|---|---|---|---|---|---|---|
| 30 | 31.5 | 30.7 | 29.3 | 28.6 | 27.9 | 27.2 |
| 35 | 36.6 | 35.8 | 34.2 | 33.5 | 32.7 | 32.0 |
| 40 | 41.8 | 40.9 | 39.2 | 38.3 | 37.5 | 36.7 |
| 45 | 46.9 | 46.0 | 44.1 | 43.2 | 42.3 | 41.4 |
| 50 | 52.1 | 51.0 | 49.0 | 48.0 | 47.0 | 46.1 |
| 55 | 57.3 | 56.1 | 53.9 | 52.8 | 51.8 | 50.7 |
API MPMS 11.1 uses a base-density iteration: from the observed density it computes α₆₀ and CTL, divides observed density by CTL to estimate ρ₆₀, and repeats (~5 passes) until converged, then reports API@60.
Liquids are less dense when warm, so a hydrometer reads higher API at high temperature than the true 60 °F value. The correction removes this effect.
Measurement: API MPMS Ch. 9.1 (ASTM D1298). Reduction to 60 °F: API MPMS Ch. 11.1 (ASTM D1250).
Yes — the chart above lists corrected API gravity at 60 °F for observed readings of 30–55 °API taken at 40–100 °F, for generalized crude oil per API MPMS Ch. 11.1. A reading above 60 °F corrects downward; below 60 °F, upward. For exact, commodity-specific values, use the calculator.