Brewing ABV Calculator

Enter the original gravity measured before fermentation.

Enter the final gravity after fermentation has finished and the reading is stable.

The calculator estimates alcohol by volume, apparent attenuation, and the drop in specific gravity.

Use temperature-corrected hydrometer readings or properly corrected post-fermentation refractometer values.

Original gravity, abbreviated OG, is the specific gravity of the wort or must before fermentation.

Final gravity, abbreviated FG, is the reading after fermentation when yeast has consumed part of the available fermentable material.

The reduction in gravity provides a practical way to estimate the alcohol created during fermentation.

The calculator multiplies the difference between OG and FG by 131.25.

For example, an OG of 1.050 and FG of 1.010 produce a gravity drop of 0.040 and an estimated 5.25% ABV.

This equation is widely used for practical homebrewing calculations because it is simple and produces a useful estimate for ordinary fermentations.

Apparent attenuation describes the percentage of original gravity points that disappeared during fermentation.

It is called apparent because alcohol lowers the density of the finished beverage, so the calculation does not directly represent the exact percentage of extract consumed.

Attenuation is useful for comparing fermentation performance, yeast behaviour, and recipe outcomes.

Hydrometers are calibrated for a stated temperature, commonly printed on the instrument or supplied with its instructions.

A warmer or cooler sample can produce a reading that needs correction.

Allow the sample to reach an appropriate temperature or apply the correction supplied for the specific hydrometer.

A refractometer is useful for measuring sugar concentration before fermentation.

Once alcohol is present, the displayed Brix or specific-gravity scale no longer behaves like an ordinary unfermented reading.

Use a correction model requiring both the original and current refractometer readings before entering an equivalent final specific gravity.

Record OG before fermentation begins and before yeast changes the liquid composition.

Use a final reading that remains stable across an appropriate interval rather than relying only on expected fermentation time.

Degas carbonated samples when required by the measurement method because bubbles can interfere with instruments.

The simple gravity formula is an estimate and can diverge more as original gravity and alcohol strength increase.

Sampling, temperature, calibration, dissolved solids, carbonation, and instrument technique also affect the final value.

Professional or regulated alcohol measurement may use densitometry, distillation, real-extract analysis, gas chromatography, or another validated laboratory method.

The calculation runs entirely in the browser.

Gravity readings are not uploaded, added to a public URL, or permanently stored.