About ABV & Gravity Readings
To calculate the alcohol content of your homebrew, you need two measurements: the Original Gravity (OG) taken before fermentation begins, and the Final Gravity (FG) taken after fermentation is complete.
The ABV Formula
The simplest and most widely used formula is:
ABV = (OG − FG) × 131.25
For example, a beer with OG 1.050 and FG 1.012 has: (1.050 − 1.012) × 131.25 = 4.99% ABV.
Specific Gravity vs Plato/Brix
Specific Gravity (SG) measures the density of wort relative to water (e.g., 1.050). Plato (°P) and Brix (°Bx) express the sugar content as a percentage by weight. For most homebrewing, 1°P ≈ 0.004 SG. This calculator converts between both systems automatically.
Beer vs Wine vs Mead
The ABV formula works identically for all fermented beverages. Typical ranges: Beer OG 1.040–1.070 (4–8% ABV), Wine OG 1.070–1.100 (10–14% ABV), Mead OG 1.080–1.140 (8–18% ABV).
Attenuation
Apparent attenuation shows how much of the sugar was consumed by yeast: ((OG − FG) / (OG − 1)) × 100. Most beer yeasts attenuate 70–80%. Real attenuation accounts for the lower density of alcohol and is approximately 81% of apparent attenuation.