How to calculate beer ABV from OG and FG

What ABV means

Alcohol by volume (ABV) is the percentage of ethanol in your finished beer. Brewers estimate it from the drop in density between original gravity (before fermentation) and final gravity (after fermentation). Yeast converts sugars into alcohol and CO₂, so a larger gravity drop usually means higher ABV.

Step 1: Measure original gravity (OG)

Cool a wort sample and measure with a hydrometer or refractometer before pitching yeast. Record the reading as Specific Gravity (for example 1.050) or degrees Plato. Temperature matters — correct hydrometer readings to the instrument's calibration temperature.

Step 2: Measure final gravity (FG)

When fermentation is finished and gravity is stable for a few days, take another sample. Measure FG before adding priming sugar for bottling. Priming sugar adds fermentables and would inflate ABV if included in FG.

Step 3: Apply an ABV formula

Standard formula

Example: OG 1.050, FG 1.010 → 0.040 × 131.25 = 5.25% ABV. This is the default most homebrewers use.

Alternate Hall formula

Use this for stronger beers where the simple constant underestimates alcohol. The same 1.050 / 1.010 example returns about 5.34% ABV.

Prefer not to do the math by hand? Use our free ABV calculator — it supports SG and Plato plus both equations.

Check attenuation and calories

Apparent attenuation shows fermentation efficiency:

For OG 1.050 / FG 1.010 you should see about 79% attenuation and roughly 163.7 calories per 12 oz using the ASBC Beer-33 calorie method.

Common mistakes

• Skipping temperature correction on hydrometer samples
• Using a refractometer FG without alcohol correction
• Measuring FG after priming sugar is added
• Mixing Plato and SG values in the same formula
• Expecting lab-perfect ABV from approximate home readings

Try it now

Open the CalculatorMint ABV calculator and enter your OG and FG. Results update instantly with ABV, attenuation, calories, and dual-unit gravity readouts.