Brew Lab · Calculators I + II
Apparent Attenuation Calculator
Compare original and final hydrometer gravity as apparent attenuation, or rearrange the same relationship for a planning-only final-gravity estimate.
Boundary: Do not use a predicted final gravity as proof that fermentation is complete before sealed packaging.
Static result contract
Worked example
A production ICU form can progressively enhance this calculator later. The method and representative result remain understandable with no JavaScript.
- Apparent attenuation
- 80.0%
- Gravity points consumed
- 40.0
- Remaining points
- 10.0
Method
Formula is part of the interface
BEU does not hide the calculation behind a single result number.
| Method | Formula | Interpretation boundary |
|---|---|---|
| Apparent attenuation | AA% = [(OG − FG) / (OG − 1)] × 100 | Hydrometer apparent attenuation is affected by alcohol density and is not identical to real attenuation/extract. |
| Planning-only final gravity | FG = OG − (OG − 1) × AA | Algebraic rearrangement; does not predict how a real fermentation will finish. |
Input contract
Units and guards
Input guards keep this foundation implementation bounded. They are not style definitions, legal thresholds, or equipment ratings.
| Input | Accepted units / range | Boundary |
|---|---|---|
| Original gravity | specific gravity | Measured SG before fermentation. |
| Final gravity | specific gravity | Measured SG after fermentation for observed apparent attenuation. |
Limits & safety
What the result does not prove
Limitations
- Apparent attenuation is not a literal sugar-consumption percentage.
- A target attenuation does not guarantee an actual final gravity.
Safety / responsible-use notes
- Do not use a predicted final gravity as proof that fermentation is complete before sealed packaging.
Methodology sources
Follow the method back to its references
External formulas and technical claims are sourced separately from Beer Universe's own algebra, unit handling, and interface policy.
- BJCP legacy study guide — attenuation explanation
organization primary · legacy brewing education · apparent attenuation explanation · gravity and fermentation context - Brewer's Friend ABV Calculator methodology
reputable secondary · standard hydrometer ABV approximation · alternate hydrometer ABV approximation · gravity-reading methodology context - BEU017 Brew Lab methodology contract
beu original · BEU unit conversion implementation · BEU calculator input guards · BEU route and result-state policy · BEU algebraic scaling and rearrangement