ABV Calculator
Work out alcohol by volume from the original and final gravity of a brew — with the attenuation that tells you how far fermentation actually went.
Fermentation converts sugar into alcohol and carbon dioxide, so the liquid gets lighter.
How the abv calculator works
Fermentation converts sugar into alcohol and carbon dioxide, so the liquid gets lighter. Measuring specific gravity before and after gives the drop, and the standard approximation multiplies it by 131.25 to get ABV. A more accurate formula, used here for stronger brews, corrects for the fact that the simple version overstates alcohol above about 6%.
Apparent attenuation is the share of the sugar consumed. Most ale yeasts finish at 70–80%; much below that suggests a stalled fermentation, and much above it a very dry beer or a wine yeast that kept going.
Formula: ABV ≈ (OG − FG) × 131.25; attenuation = (OG − FG) ÷ (OG − 1)
Worked examples
| Inputs | Alcohol by volume | Note |
|---|---|---|
| OG 1.050 to FG 1.010 | 5.34 % | 5.25% by the simple rule, 5.3% corrected |
| A strong ale, 1.080 to 1.018 | 8.7 % | about 8.3% |
| A session beer, 1.038 to 1.008 | 3.93 % | about 3.9% |
FAQFrequently asked questions
How do I calculate ABV?
Subtract the final gravity from the original and multiply by 131.25. This page also shows a corrected figure, which is more accurate above about 6%.
What is specific gravity?
The density of the liquid compared with water. Sugar makes it heavier, so 1.050 means 5% denser than water.
What is attenuation?
The proportion of fermentable sugar the yeast consumed. Most ale yeasts reach 70–80%.
Why do the two formulas disagree?
The simple one is a linear approximation fitted to ordinary beer strengths. Above about 6% it drifts, so the corrected form is better for strong brews.
My fermentation seems stuck — what now?
Check the temperature first, then rouse the yeast gently. A gravity that has not moved in three days at the right temperature is genuinely finished, however high it reads.
Where these figures come from
- US FDA — Safe Minimum Internal Temperatures — the internal temperatures the roasting calculator targets
- NIST SP 811 — Guide for the Use of the International System of Units — the exact weight and volume conversions used throughout
- UK Food Standards Agency — food safety and labelling standards
Last checked: September 2026. Baking ratios follow standard baker's percentage practice; roasting guidance follows published safe internal temperatures.