Brewing ABV Calculator

What this calculator estimates and when to use it

Alcohol by volume (ABV) in home brewing is estimated from how much the fermentable sugar in your wort converted into alcohol, which you track indirectly through specific gravity — a measurement of how much denser your liquid is than water. Before fermentation, sugar dissolved in the wort makes it denser than water, giving an Original Gravity (OG) reading above 1.000 (typically 1.040–1.090 for beer). As yeast consumes sugar and produces alcohol and CO₂, the liquid gets less dense, so the Final Gravity (FG) reading drops. The size of that drop is what both ABV formulas below are built from.

Use this calculator after taking hydrometer or refractometer readings before pitching yeast (OG) and again once fermentation has finished and stabilized over 2-3 days (FG). It's built for home brewers checking a batch of beer, cider, or mead — not for distilled spirits, which involve a completely different concentration process after fermentation.

The two formulas and what they mean

Standard formula: ABV = (OG − FG) × 131.25

Advanced formula: ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794)

Where OG is Original Gravity and FG is Final Gravity, both measured as specific gravity (e.g., 1.050). The standard formula is a simple linear approximation that's accurate enough for most everyday beers. The advanced formula accounts for the fact that alcohol and sugar affect liquid density differently, which matters more as OG climbs — it's generally more accurate for higher-gravity beers (OG above roughly 1.070), where the standard formula tends to overestimate ABV. The calculator also reports Apparent Attenuation — the percentage of the gravity drop relative to how far OG is above 1.000, or (OG−FG)/(OG−1)×100 — which tells you how thoroughly your yeast fermented the available sugar.

Worked example

For an OG of 1.050 and FG of 1.010 (a typical session beer): Standard ABV = (1.050 − 1.010) × 131.25 = 0.040 × 131.25 = 5.25%. Advanced ABV = 76.08 × 0.040 ÷ (1.775 − 1.050) × (1.010 ÷ 0.794) = 3.0432 ÷ 0.725 × 1.2720 ≈ 5.34%. Apparent Attenuation = (0.040 ÷ 0.050) × 100 = 80.0%. Entering OG=1.050 and FG=1.010 into the calculator above reproduces all three figures exactly.

Common mistakes and how to interpret the result

• Taking the FG reading too early. Fermentation can appear to slow down before it's truly finished — take FG readings on two consecutive days at least 2-3 days apart and confirm they match before trusting the number.
• Not correcting for temperature. Hydrometers are calibrated to a reference temperature (often 60°F/15.6°C) — reading a hot or cold sample without a temperature correction skews both OG and FG, and that error carries straight into the ABV calculation.
• Using the standard formula for very high-gravity beers. For imperial stouts, barleywines, or other beers with OG above about 1.070, the standard formula noticeably overestimates ABV — favor the advanced formula's result in that range.
• Treating attenuation as a quality score. Attenuation depends heavily on yeast strain, mash temperature (for all-grain brewing), and fermentable sugar mix — a lower attenuation isn't automatically a mistake, and a higher one isn't automatically better beer.

Frequently Asked Questions

Common Tip Percentages

General Household Budget Ratios (50/30/20 Rule)

Common Measurement Conversions for Everyday Use