Free tool
Enter your original and final gravity to work out your brew's alcohol by volume (ABV) and how far it fermented. Works for beer, wine, mead, cider and country wine.
The standard homebrew formula is:
Take a hydrometer reading before pitching your yeast — that's your original gravity — and another once fermentation has finished, your final gravity. The bigger the drop between them, the more sugar your yeast turned into alcohol. This calculator also shows apparent attenuation: how much of the available sugar fermented out.
The standard homebrew formula is ABV = (OG − FG) × 131.25. Subtract your final gravity from your original gravity and multiply by 131.25 for an approximate alcohol by volume.
Original gravity (OG) is the density of your wort or must before fermentation; final gravity (FG) is the density once the yeast has finished. The drop between them shows how much sugar was converted to alcohol.
Apparent attenuation is the percentage of sugar the yeast fermented, calculated as (OG − FG) / (OG − 1) × 100. Higher attenuation means a drier finish.
The × 131.25 formula is a good approximation for most homebrew up to around 10% ABV. For stronger wines and meads it can read slightly low, but it remains the most widely used quick estimate.
Demijohn Journal works out ABV for you as you log gravity readings — and keeps your recipes and full fermentation history in one place. Free.
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