Free Homebrew ABV Calculator

Enter your original gravity (OG) and final gravity (FG) from a hydrometer, original and final Brix from a refractometer, or just final hydrometer and refractometer readings if you missed the OG, to estimate the alcohol by volume (ABV) of your beer, mead, cider, or wine.

Last updated October 15, 2026

How the calculator works

Fermentation turns sugar into alcohol, so the drop in density between the start and end of fermentation indicates how much alcohol was made. The calculator uses one of two widely used formulas depending on the beverage type you pick — the same formulas as the BrewNote app.

Standard formula (beer and kombucha)

ABV = (OG − FG) × 131.25

Worked example: OG 1.050 and FG 1.010 gives (1.050 − 1.010) × 131.25 = 5.25% ABV, with 80% apparent attenuation (the share of sugar the yeast consumed).

Alternate formula (mead, cider, and wine)

ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794)

Meads, ciders, and wines often start at much higher gravities, where the simple linear formula is less accurate, so the calculator uses the alternate formula for them. The two agree closely at low gravity: at OG 1.050 / FG 1.010 the alternate formula gives 5.34%. They diverge at high gravity: a mead at OG 1.110 finishing at FG 1.000 comes out at 14.4% with the standard formula and 15.8% with the alternate.

Using a refractometer

A refractometer reads wort slightly higher than a pure sugar solution, so the calculator first divides both readings by your wort correction factor (default 1.04). Before fermentation there’s no alcohol, so the corrected original Brix converts directly to specific gravity. After fermentation, alcohol distorts the reading, so the calculator applies Sean Terrill’s cubic correction, which uses both the original gravity and the final Brix, to estimate the true FG. Measure your own wort correction factor if you can; the default is only a starting point. Refractometer FG estimates are less certain than hydrometer readings, so confirm with a hydrometer when precision matters.

No original gravity reading

Forgot to take an OG? Take a hydrometer reading and a refractometer reading of the same finished sample. The hydrometer gives the true final gravity, while alcohol skews the refractometer. The calculator runs the same refractometer correction in reverse to find the original gravity that explains the gap between the two, then computes ABV from that estimated OG and the hydrometer FG.

Terms used

• Original gravity (OG): specific gravity measured before the yeast is added.
• Final gravity (FG): specific gravity once fermentation has finished.
• Hydrometer: a floating glass instrument that reads specific gravity directly from a sample.
• Refractometer: an optical instrument that reads dissolved sugar in degrees Brix from a few drops of liquid.
• Brix: a measure of sugar concentration by weight; roughly 1 °Bx is 1 gram of sugar per 100 grams of solution.

New to gravity readings? See Specific gravity for homebrewing.

Limitations

• The result is an estimate of ABV by volume, not a laboratory measurement.
• Hydrometers are calibrated at a specific temperature. Warm samples read low in density; correct for temperature or cool the sample first.
• Dissolved CO₂ and bubbles cling to a hydrometer and can inflate the reading; degas the sample.
• Sugar added after the original reading (fruit, honey, or priming sugar) is not captured unless you adjust the OG.
• Unfermented sugars, back-sweetening, and high-gravity ferments all reduce accuracy.

References

• American Homebrewers Association — How to take an accurate hydrometer reading
• Brewer’s Friend — Alcohol by volume calculator (standard and alternate formulas)
• Homebrewers Association forum — Improved refractometer correction calculator
• John Palmer — How to Brew