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Homebrew ABV Calculator

Calculate a homebrewed beer, wine, or mead's alcohol by volume from its original and final gravity readings, using both the standard and high-gravity formulas.

ABV (simple formula)
5.25%
ABV (Hall/Balling formula)
5.34%
Difference between formulas
0.09 pts

How it works

The standard homebrewing shortcut is ABV% = (OG − FG) × 131.25, treating alcohol production as roughly proportional to how far gravity drops during fermentation. It's accurate to within about ±0.3% for typical beers, but the true relationship isn't quite linear, so this shortcut increasingly underestimates ABV at high gravity.

For a more accurate figure at high gravity, this calculator also applies Dr. Michael Hall's 1995 formula (derived from the Balling equation): it first computes alcohol by weight, ABW = 76.08 × (OG − FG) ÷ (1.775 − OG), then converts to alcohol by volume using ethanol's density, ABV = ABW × (FG ÷ 0.794). The two formulas agree closely below about 8% ABV and diverge more noticeably above it.

Both results are shown side by side so you can see how much they agree for your specific gravity readings, rather than picking one formula and hiding the difference.

FAQ

Why do I get two different ABV numbers?

The simple (OG − FG) × 131.25 formula is a linear approximation that works well for typical beers but drifts as original gravity climbs into high-gravity territory (imperial stouts, barleywines, high-gravity meads). The Hall/Balling formula accounts for that non-linearity, so the two numbers converge for ordinary-strength brews and spread apart for big, high-OG batches.

What if my final gravity is still slowly dropping?

Take the final gravity reading only once it holds steady across several consecutive days — fermentation isn't finished until gravity stops changing, and an ABV calculated from a still-fermenting FG will read lower than the beer's eventual actual strength.

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