API Gravity Calculator

Because specific gravity (SG) sits in the DENOMINATOR of the formula °API = (141.5 / SG) - 131.5. As SG gets smaller (the oil is lighter, closer to or less dense than water), 141.5/SG gets larger, which pushes the final API gravity number up. This inverse relationship is why "light" crude oils have HIGH API gravity numbers (typically above 31) while "heavy" crudes have low numbers -- it can feel backwards at first since higher API gravity means lower density.

Petroleum, like most liquids, expands and becomes slightly less dense as it warms, which shifts the raw specific gravity reading depending on when and where it was measured. This calculator corrects that using a simplified linear approximation of the standard temperature-correction procedure, adjusting every reading back to the industry-standard reference temperature of 60°F so that two samples measured on a hot day and a cold day can be compared on equal footing. A sample measured warmer than 60°F reads LOWER specific gravity than it truly has at the reference temperature, so the correction adds back what the warmth subtracted; a sample measured colder than 60°F gets a small downward correction instead.

This calculator classifies corrected API gravity above 31.1° as Light, 22.3-31.1° as Medium, 10-22.3° as Heavy, and below 10° as Extra Heavy. These bands follow commonly-used industry conventions; light crudes generally command a price premium because they yield a higher proportion of valuable refined products like gasoline with less refining effort than heavy crudes do.

No -- the Uncorrected API Gravity output is calculated directly from the specific gravity you entered, with no temperature adjustment applied at all. Only the Corrected API Gravity (at 60°F) result, along with the Corrected Specific Gravity, Density, and Barrels per Metric Ton figures, factor in the Observed Temperature input.