Brew Lab · Calculators I + II
Gravity & ABV Calculator
Estimate alcohol by volume from measured original and final specific gravity while showing both common hydrometer formulas and apparent attenuation.
Boundary: The calculation describes beverage strength; it is not a serving recommendation or health-risk threshold.
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.
- Standard ABV
- 5.25%
- Alternate ABV
- 5.34%
- Apparent attenuation
- 80.0%
Method
Formula is part of the interface
BEU does not hide the calculation behind a single result number.
| Method | Formula | Interpretation boundary |
|---|---|---|
| Standard hydrometer ABV approximation | ABV% = (OG − FG) × 131.25 | Widely used approximation for hydrometer readings; not a laboratory alcohol assay. |
| Alternate hydrometer ABV approximation | ABV% = [76.08 × (OG − FG) / (1.775 − OG)] × (FG / 0.794) | Alternative approximation useful for comparison when gravity is high; formula choice does not eliminate measurement uncertainty. |
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 · 0.98 to 1.25 | Hydrometer-style specific gravity; temperature correction is outside this BEU017 tool. |
| Final gravity | specific gravity · 0.97 to 1.25 | Use a properly corrected measurement; refractometer readings after fermentation require a separate correction method. |
Limits & safety
What the result does not prove
Limitations
- Estimated from gravity change rather than direct ethanol measurement.
- Reading/calibration/temperature error propagates into ABV.
- Post-fermentation refractometer values are not accepted as raw SG in this foundation tool.
Safety / responsible-use notes
- The calculation describes beverage strength; it is not a serving recommendation or health-risk threshold.
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.
- Brewer's Friend ABV Calculator methodology
reputable secondary · standard hydrometer ABV approximation · alternate hydrometer ABV approximation · gravity-reading methodology context - BJCP legacy study guide — attenuation explanation
organization primary · legacy brewing education · apparent attenuation explanation · gravity and fermentation 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