Estimate ABV from original and final gravity

Estimate homebrew alcohol by volume and apparent attenuation from paired gravity readings.

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ToolABV Calculator
Input
Output
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How it works

Original gravity minus final gravity is multiplied by 131.25 for the common homebrew ABV estimate. Apparent attenuation divides the gravity-point drop by original gravity points above 1.000.

Formula
estimated ABV % = (OG − FG) × 131.25
  • Both readings are required and original gravity must exceed water’s 1.000 reference.
  • No temperature or refractometer correction is silently applied.

Worked example

A typical pale ale
Original gravity 1.050, final gravity 1.010
Input
											Original gravity: 1.05
Final gravity: 1.01
Output
												ABV: 5.25
Attenuation: 80

When to use this

Beer logs compare pre-fermentation and stable final gravity, cider and mead trials estimate batch strength, and apparent attenuation compares yeast performance.

Edge cases

  • A final refractometer reading is distorted by alcohol and needs a brewing correction before it can be entered as specific gravity.
  • A hydrometer sample away from its calibration temperature needs instrument-specific correction; the entered readings are used unchanged.
  • Final gravity above original gravity is rejected because the formula would imply negative fermentation.

References