ABV calculator
The classic 131.25 multiplier is a linear approximation. It drifts high above about 7% and there is a better fit.
Alcohol by volume
5.791%
- By the simple 131.25 formula
- 5.644 %
- Alcohol by weight
- 4.604 %
- Apparent attenuation
- 78.18 %
- Original gravity in Plato
- 13.570
- Final gravity in Plato
- 3.068
- Calories per 355 mL
- 290 kcal
Show the working
- Original gravity = 1.055
- Final gravity = 1.012
- diff = 1.055 - 1.012 = 0.043
- By the simple 131.25 formula = 0.043 * 131.25 = 5.643 75
- Alcohol by volume = (76.08 * 0.043 / (1.775 - 1.055)) * (1.012 / 0.794) = 5.791 17
- Alcohol by weight = 5.791 17 * 0.795 = 4.603 98
- Apparent attenuation = (1.055 - 1) > 0 ? 0.043 / (1.055 - 1) * 100 : 0 = 78.1818
- Original gravity in Plato = (-1 * 616.868) + (1111.14 * 1.055) - (630.272 * 1.055^2) + (135.997 * 1.055^3) = 13.5695
- Final gravity in Plato = (-1 * 616.868) + (1111.14 * 1.012) - (630.272 * 1.012^2) + (135.997 * 1.012^3) = 3.068 27
- Calories per 355 mL = (6.9 * 4.603 98 + 4 * (13.5695 - 0.1 * 13.5695)) * 1.012 * 3.55 = 289.627
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- simple: ABV = (OG - FG) x 131.25
- better fit: ABV = (76.08 (OG - FG) / (1.775 - OG)) x (FG / 0.794)
- apparent attenuation = (OG - FG) / (OG - 1)
Attenuation above about 85% usually means either a very simple wort or a wild yeast.
Both formulas are empirical. Hydrometers also read gravity, not alcohol, and alcohol is less dense than water — which is what the correction accounts for.