Alcohol by volume from two readings
Brewers measure how much sugar a liquid holds before fermentation (the original gravity, OG) and after it (the final gravity, FG). The drop between the two shows how much sugar the yeast turned into alcohol. This ABV calculator turns those readings into alcohol by volume for beer, wine, cider and mead, and it accepts specific gravity, °Plato or °Brix, with a correction for refractometer readings taken after fermentation has started.
It is a maths tool for people who make fermented drinks at home or study the process, and it does not encourage drinking. The result is an estimate from a hydrometer or refractometer, not a laboratory analysis, and strength on a commercial label is set by testing and by local law.
How to use the ABV Calculator
- Enter the original reading and choose its unit: specific gravity such as 1.050, °Plato or °Brix.
- Enter the final reading. For a refractometer reading of a fermented sample, choose the refractometer unit and the correction is applied.
- Pick the simple or advanced formula and read the ABV.
- Check the detail list for attenuation, alcohol by weight and the readings converted to SG and °Plato.
ABV Calculator features
SG, Plato and Brix
Any of the three scales for the original reading, converted to specific gravity before the sum.
Two formulas
The familiar (OG − FG) × 131.25 and a more accurate higher-gravity formula, both shown so you can compare.
Refractometer correction
A cubic correction for Brix readings of a fermented sample, because alcohol bends light and makes the raw reading look too high.
Brix table
A ten-row table of Brix, specific gravity and potential alcohol for juice, must and honey-water.
The formulas
The simple formula is ABV = (OG − FG) × 131.25. It is accurate enough for beers up to about 6–7%. For stronger drinks the advanced formula, ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794), as published by BeerSmith and Brewer’s Friend, follows the real behaviour more closely. At 1.050 to 1.010 they give 5.25% and 5.34%; at 1.120 to 1.000 the gap is larger.
Alcohol by weight is 0.79 × ABV ÷ FG, and apparent attenuation, the share of the original extract that disappeared, is (OG − FG) ÷ (OG − 1). The Plato to SG conversion is SG = 1 + P ÷ (258.6 − (P ÷ 258.2) × 227.1), and the reverse uses a cubic in SG. These are the standard brewing approximations, taken from published brewing references; they were not re-checked against a standards body for this page.
Brix, Plato and refractometers
Degrees Brix and degrees Plato are nearly the same scale: percent sugar by weight in water. A refractometer reads Brix of the liquid by how it bends light. After fermentation begins, alcohol also bends light, so the raw number overstates the sugar. The page applies the Terrill cubic equation to the original and final Brix to estimate the true final gravity. Use it only for fermented samples, and measure the original reading with the same instrument. A hydrometer reading is simpler and does not need this correction.
Getting good readings
- Degas and cool the sample. Bubbles lift a hydrometer and warm liquid is thinner than the calibration temperature assumes.
- Take readings on consecutive days. A final gravity that holds steady for three days means fermentation has finished.
- Subtract additions. Fruit, honey or sugar added late changes the true original gravity; use a reading taken after the last addition.
- Know the limits. Yeast, dissolved solids and unfermentable sugars all affect the result by a few tenths of a percent.
Local rules
Making beer or wine for personal use is legal in many countries, including the United States and the United Kingdom, within limits that differ by place. In India the rules are set by each state’s excise department and vary widely. Distilling is a separate matter and is restricted almost everywhere. Check the rules where you live. To compare drinks by strength, see the alcohol unit calculator; for carbonation, the priming sugar calculator.
ABV Calculator FAQ
How do I calculate ABV from OG and FG?
Subtract the final gravity from the original gravity and multiply by 131.25. An OG of 1.050 and an FG of 1.010 gives 0.040 × 131.25 = 5.25%.
Which ABV formula is more accurate?
The advanced formula is closer for drinks above about 7% such as strong ales, wine and mead. For ordinary beers the simple formula is within a few tenths of a point.
Can I use Brix instead of specific gravity?
Yes. Choose °Brix as the unit and the tool converts it to specific gravity. If you measured the final value with a refractometer after fermentation began, choose the refractometer unit so the correction applies.
Why is my refractometer final reading wrong?
Alcohol changes how light bends, so a fermented sample reads higher than its true sugar content. The cubic correction uses both the starting and final Brix to remove that error.
Does this work for wine, cider and mead?
Yes. The maths depends only on gravity. Wine and mead start at higher gravities, so use the advanced formula and a hydrometer when you can.
Is this the same as the alcohol unit calculator?
No. This page estimates the strength of something you fermented. The alcohol unit calculator converts a drink’s strength and size into units.