Attenuation Calculator
Apparent and real attenuation from OG/FG, or predict FG from a target attenuation.
From OG and FG
- apparent
Real attenuation-
Predict FG from target attenuation
FG ≈ -
How it works
Attenuation is the fraction of available sugar the yeast consumed, measured as the drop in gravity points. Real attenuation applies the standard correction for the alcohol that fools a hydrometer.
apparent % = (OG − FG) / (OG − 1) × 100
FG = OG − (OG − 1) × attenuation
Source: Brewer's Friend attenuation calculator.
Apparent attenuation is what a hydrometer reads (alcohol skews it high); real attenuation corrects for that. Both are planning figures - your actual finish depends on yeast, grist and temperature.
Frequently asked questions
- What is apparent vs real attenuation?
- Apparent attenuation is the gravity drop measured by a hydrometer, which reads low because alcohol is present - so the figure looks higher than the true fermentation. Real attenuation corrects for alcohol and is about 81% of apparent. Brewers usually quote apparent attenuation.
- How do I predict final gravity from attenuation?
- If you know your yeast's typical apparent attenuation, enter it with your OG and the tool predicts FG: FG = OG − (OG − 1) × attenuation. Useful for planning a beer's strength and dryness before you brew.