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ABV Calculator

Find the ABV of your beer or wine from gravity readings.

Result

5.25%
80.00%

How it is calculated

The tool applies the simple brewing formula ABV = (OG − FG) × 131.25, where OG is the original gravity measured before fermentation and FG the final gravity after it, both as hydrometer specific-gravity readings such as 1.050. It also reports apparent attenuation, the share of the available sugar that yeast consumed: attenuation = (OG − FG) / (OG − 1) × 100.

OG must be above 1, FG must be positive and not higher than OG, otherwise there is no result. Enter gravity as 1.050, not as 50 or as degrees Plato. The 131.25 factor is an approximation that works well for ordinary beer strengths and drifts for very strong brews. Readings should be temperature-corrected first.

Worked example

A beer starts at OG 1.050 and finishes at FG 1.010. The drop is 1.050 − 1.010 = 0.040. ABV = 0.040 × 131.25 = 5.25%. Of the 0.050 of sugar-related gravity above water, 0.040 was fermented, so apparent attenuation is 0.040 / 0.050 × 100 = 80.00%.

Try this example →

Common mistakes

  • Swapping OG and FG. The tool rejects a final gravity higher than the original, but two close readings in the wrong columns still give a misleading figure.
  • Typing gravity as 1050 or 50 (the "gravity points" shorthand) instead of 1.050.
  • Taking the reading from a warm or CO2-filled sample. Temperature and bubbles shift a hydrometer reading, so cool and degas the sample first.
  • Calling the apparent attenuation the real one. Alcohol lowers density, so true attenuation is somewhat lower than the apparent figure shown here.

About this calculator

This calculator finds the alcohol by volume (ABV) of home-brewed beer or wine from the original gravity (OG) and final gravity (FG) readings taken with a hydrometer, using the standard formula ABV = (OG − FG) × 131.25; this is a simple approximation that drifts for very strong brews. It also reports apparent attenuation, the percentage of sugars converted to alcohol.

Homebrewers and winemakers take these gravity readings before and after fermentation to confirm fermentation finished and to know the strength of the finished batch for labeling or recipe adjustment.

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Comments (1)

  • Editorial team

    Dry wines and ciders often finish below 1.000, and the tool accepts that. An OG of 1.090 and FG of 0.995 gives about 12.47 percent ABV and an attenuation above 100 percent, which is normal because alcohol is lighter than water and pulls the reading down. To judge that fermentation is truly finished, take the final gravity on two or three days in a row and see that it holds steady. What are you brewing?

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