ABV Calculator (Alcohol by Volume)
Free ABV calculator: enter OG and FG for alcohol by volume via (OG − FG) × 131.25 plus a high-gravity formula, ABW, calories, and attenuation %.
Punch your original gravity (OG) and final gravity (FG) into the calculator above and it returns your beer’s alcohol by volume two ways: the standard homebrew formula, ABV = (OG − FG) × 131.25, and a high-gravity alternate that stays accurate above roughly 6.5% alcohol. It also reports ABW (about ABV × 0.79), an estimated calorie count per 12 oz pour, and apparent attenuation, which is (OG − FG) ÷ (OG − 1). The classic example: a pale ale that starts at 1.050 and finishes at 1.010 works out to 0.040 × 131.25 = 5.25% ABV, 80% apparent attenuation, and roughly 165 calories per 12 oz. Two hydrometer readings are all you need — everything else is arithmetic. The sections below cover what those readings actually measure, why 131.25 works (and when it quietly under-reports), and how to take samples the math can trust.
How do you calculate ABV?
Subtract final gravity from original gravity and multiply by 131.25: ABV = (OG − FG) × 131.25. A beer that starts at 1.050 and finishes at 1.010 is 0.040 × 131.25 = 5.25% ABV. For beers above roughly 6.5%, the more accurate formula is ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794); the calculator above runs both automatically.
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ABV Calculator
Key Information
| Parameter | Details |
|---|---|
| Standard formula | ABV = (OG − FG) × 131.25 |
| High-gravity formula (Hall, Zymurgy 1995) | ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794) |
| Apparent attenuation | (OG − FG) ÷ (OG − 1) × 100, typically 70–80% for ale yeast |
| Federal homebrew limit (26 U.S.C. §5053(e)) | 100 gal/year for a 1-adult household; 200 gal/year with 2+ adults |
Frequently Asked Questions
How do you calculate ABV?
Subtract final gravity from original gravity and multiply by 131.25: ABV = (OG − FG) × 131.25. A beer that starts at 1.050 and finishes at 1.010 is 0.040 × 131.25 = 5.25% ABV. For beers above roughly 6.5%, the more accurate formula is ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794); the calculator above runs both automatically.
What’s the difference between ABV and ABW?
ABV measures the volume of ethanol per volume of beer; ABW measures its weight per weight of beer. Because ethanol is lighter than water (0.789 g/mL), ABW is always the smaller number — roughly ABW = ABV × 0.79 at normal beer strength, which is the conversion this calculator uses. A 5.0% ABV beer is about 4.0% ABW. A few US states historically regulated beer strength in ABW, which is why both units still appear.
Why does my refractometer give a different FG than my hydrometer?
Because alcohol distorts refractometer readings. A refractometer measures how much light bends through a sample, and ethanol bends light more than the sugar-only calibration assumes, so post-fermentation readings run high — an uncorrected reading can show roughly 1.020 when a hydrometer shows 1.010. Use a refractometer for OG, then either a hydrometer or an alcohol-corrected conversion for FG before entering numbers in the calculator above.
Are these calculators free to use?
Yes, all calculators on CalcCorp are completely free — no registration, no login, no hidden charges. Results are calculated instantly in your browser and we do not store any of your data.
How accurate are these calculations?
Our calculators use standard financial formulas updated with the latest tax rates, interest rates, and government policies for 2026. Results are accurate for planning purposes but should be verified with a professional for final decisions.
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Last updated: March 2026