ABV Calculator
Estimate alcohol by volume from original gravity and final gravity
Estimate alcohol by volume from original gravity and final gravity. The formula is (OG − FG) × 131.25. This is a brewing estimate from a hydrometer, not a lab alcohol test. To dilute a spirit to a target strength, use the alcohol dilution calculator.
Calculator Inputs
Hydrometer reading before fermentation
Hydrometer reading after fermentation
Results
Enter values above to see your results
How to use this calculator
- Enter the original gravity from before fermentation.
- Enter the final gravity from after fermentation.
- Read ABV and apparent attenuation. Original gravity must be higher than final gravity.
How the calculation works
Each gravity point that fermentation removes stands in for a small amount of alcohol. Multiplying the drop by 131.25 is the usual simple estimate. An original gravity of 1.050 and a final gravity of 1.010 drop by 0.040, and 0.040 × 131.25 is 5.25% ABV.
Apparent attenuation is the share of the original extract that the hydrometer says was fermented: (OG − FG) ÷ (OG − 1).
Gravity points, not proof
Enter specific gravity, such as 1.050, not Plato or Brix, and not proof. Proof is twice the alcohol percent of a distilled spirit and uses a different measurement.
Worked example
OG 1.050 and FG 1.010
1.050 − 1.010= 0.0400.040 × 131.25= 5.25%0.040 ÷ 0.050= 80%Tips & Best Practices
- •Take both readings at the same temperature the hydrometer is calibrated for, often 60°F or 68°F.
- •Final gravity has to be lower than original gravity. A higher final reading usually means a typo or an unfinished fermentation.
Frequently Asked Questions
How do you calculate ABV from OG and FG?
Subtract final gravity from original gravity and multiply by 131.25. A drop from 1.050 to 1.010 is 5.25% ABV.
What is apparent attenuation?
It is (OG − FG) ÷ (OG − 1), written as a percent. It describes how much of the starting gravity the hydrometer no longer sees. It is not the same number as ABV.
Can I use this for wine or cider?
Yes, if you have original and final specific gravity. It is still an estimate. A distilled spirit measured in proof needs a dilution calculation instead.