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ABV calculator

Enter your original and final gravity to get alcohol by volume, with the formula shown below. Correct readings taken warm, switch to refractometer mode if you read Brix, and see how many standard drinks a serving holds.

Two glass hydrometers lying on a dark cloth
Photo: Agne27, CC BY-SA 3.0, via Wikimedia Commons
Units
Reading with
Temperature correction (optional)
Standard drinks (NIAAA)
Alcohol by volume—
Alternate formula—
Apparent attenuation—
OG used—
FG used—
Standard drinks per serving—
Pints to 1 drink—

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Know what’s in the glassHomebrew is often stronger than commercial beer. One US standard drink is 14 g of alcohol: 12 oz of 5% beer or 5 oz of 12% wine. Brewing and drinking are for adults 21 and over; never drink and drive.Source: NIAAA: What is a standard drink?

How it’s calculated

  1. Standard: ABV = (OG − FG) × 131.25
  2. Alternate (high gravity): ABV = 76.08 × (OG − FG) / (1.775 − OG) × (FG / 0.794)
  3. Hydrometer correction (t in °F): SGc = SG × P(t) / P(tcal), P(t) = 1.00130346 − 0.000134722124·t + 0.00000204052596·t² − 0.00000000232820948·t³
  4. Refractometer: Brixc = Brix / WCF (≈1.04); SG = 1 + Brixc / (258.6 − Brixc / 258.2 × 227.1)
  5. FG from a refractometer after fermentation (Terrill cubic): FG = 1 − 0.0044993·Ri + 0.011774·Rf + 0.00027581·Ri² − 0.0012717·Rf² − 0.00000728·Ri³ + 0.000063293·Rf³ (Ri, Rf = corrected Brix)
  6. Standard drinks (NIAAA): fl oz × ABV% / 100 / 0.6

Assumptions

  • The two ABV formulas agree below about 6% ABV; above that the alternate reads higher.
  • Most hydrometers are calibrated at 60°F (15.6°C); some read true at 68°F. Check yours.
  • Refractometer readings after fermentation need the alcohol correction and remain an approximation.

Worked example: OG 1.075, FG 1.015 → 7.88% (standard) or about 8.33% (alternate). A 1.050 reading at 80°F on a 60°F hydrometer corrects to about 1.052.

Sources: Brewer's Friend: ABV calculator (standard and alternate); Craft Beer & Brewing: hydrometer correction tool; Sean Terrill: refractometer FG results; NIAAA: What is a standard drink?

For guidance only: verify with your own readings, your equipment’s manual and the product labels.

Which ABV formula should I use?

Below about 6% ABV the standard formula, (OG − FG) × 131.25, and the alternate formula agree closely. For strong beers, wine, cider and mead the alternate formula reads higher and is usually considered closer, so the calculator shows both and you can note either in your brew log.

Hydrometer temperature correction

A hydrometer reads true only at its calibration temperature, usually 60°F (15.6°C); some read true at 68°F. Warm samples read low. The correction uses the published density polynomial for water, so it is most reliable within about 30°F of the calibration point. Cooling the sample is still the best fix.

Refractometer readings after fermentation

Alcohol bends light too, so a refractometer reads too high once fermentation starts. Refractometer mode divides your Brix by the wort correction factor (about 1.04) and estimates FG with Sean Terrill's cubic formula. Treat it as an estimate and confirm with a hydrometer before bottling.

Questions

How do I calculate ABV from OG and FG?
Subtract FG from OG and multiply by 131.25. A beer that starts at 1.050 and finishes at 1.010 is about 5.25% ABV.
Is homebrew stronger than store beer?
Often. A standard US drink is 0.6 fl oz of pure alcohol (NIAAA), which is 12 oz of 5% beer but only about 8.5 oz of a 7% IPA. The standard-drinks box shows this for your serving.
Can I use a refractometer for final gravity?
Only with an alcohol correction, and the result is an approximation. Use a hydrometer reading to confirm fermentation has finished before you bottle.

Sources

  1. Brewer's Friend: ABV calculator
  2. NIAAA: What is a standard drink?