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ABV calculator: original and final gravity

For a common beer estimate, subtract final gravity from original gravity and multiply by 131.25. An OG of 1.050 and FG of 1.010 gives approximately 5.25% ABV.

BrewMyBeer editorial · Sources checked 24 September 2026 · Calculated examples, not laboratory measurements. How we create content

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Before fermentation, for example 1.050.

A temperature-corrected density reading, for example 1.010.

Start with comparable readings

OG is the specific gravity before fermentation; FG is the reading after fermentation. Enter specific gravity as 1.050, not 50 or 12.4 °Bx. Record the actual readings rather than a recipe’s predicted values.

Check the calibration temperature printed on your hydrometer or its instructions. There is no single calibration temperature for every instrument. Correct each sample separately when necessary, remove bubbles and read the meniscus as the manufacturer specifies.

What the result tells you

The formula estimates the alcohol associated with a change in density. It is useful for recipe notes, but is not a laboratory measurement or a certification for a commercial label. Very strong beers, unusual recipes and additions made after the readings can need a different method.

Apparent attenuation compares the gravity drop with the original gravity points. It is not the percentage of every sugar molecule consumed. Alcohol changes density, so it differs from real attenuation.

Do not enter raw fermented refractometer readings

Alcohol changes refraction. A post-fermentation Brix reading needs an appropriate correction using the original reading; simply converting that Brix number to SG is insufficient. If the original reading is missing, do not manufacture an OG to make the expected ABV appear.

Before you use the result

  • OG 1.060 and FG 1.015 give about 5.91% ABV.
  • Priming sugar or later spirit additions are not included.
  • A single FG reading does not demonstrate fermentation has finished.

A quick learning check

If OG stays the same but FG is lower, what happens to the estimate?

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Sources & further reading

These references explain the methods and limitations. The worked examples and learning questions on this page are BrewMyBeer calculations, not claims of hands-on testing.