Calculate alcohol by volume (ABV) from original and final gravity.
Calculated instantly in your browser.
How is ABV (alcohol by volume) calculated?
The standard formula is ABV = (OG − FG) × 131.25, where OG is original gravity and FG is final gravity. Apparent attenuation = (OG − FG) ÷ (OG − 1). For example, an OG of 1.050 and FG of 1.010 gives about 5.25% ABV with 80% attenuation, since fermenting sugar into alcohol lowers the liquid's density.
Understanding your result
Gravity measures the density of the liquid relative to water. Sugars (denser than water) are converted to alcohol (less dense) during fermentation, so the drop from OG to FG indicates how much alcohol was produced.
Formula and method
Standard: ABV = (OG − FG) × 131.25. Advanced: ABV = (76.08 × (OG − FG) ⁄ (1.775 − OG)) × (FG ⁄ 0.794). Attenuation = (OG − FG) ⁄ (OG − 1).
Assumptions and limitations
The standard formula (OG minus FG times 131.25) is an approximation that grows less accurate at higher strengths; the advanced formula corrects for this. Both assume normal fermentation, accurate hydrometer readings and temperature-corrected gravity. Added sugars, unfermentable dextrins, or readings taken at the wrong temperature will skew the estimate.
Worked example
An OG of 1.050 and FG of 1.010 gives about 5.25% ABV by the standard formula, with 80% attenuation.
How to use this tool
- Enter the original gravity (before fermenting).
- Enter the final gravity (after fermenting).
- Read the ABV and attenuation.
Common mistakes to avoid
- Not correcting hydrometer readings for temperature.
- Swapping the original and final gravity.
About the ABV Calculator
The ABV Calculator finds the alcohol by volume of a fermented drink from its original and final specific-gravity readings, and shows the apparent attenuation.
Who should use this tool
Homebrewers and winemakers tracking fermentation.
Benefits
- Standard and advanced ABV formulas.
- Apparent attenuation percentage.
- Clear worked steps.
- Instant and private.
Practical use cases
- Checking the strength of a homebrew.
- Tracking fermentation progress.
- Comparing recipe outcomes.
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Frequently asked questions
Which formula should I use?
The standard formula is accurate for most beers up to around 6–7% ABV. For stronger brews, the advanced formula is more reliable.
What is attenuation?
The percentage of sugars the yeast converted, shown by how far the gravity dropped from OG toward 1.000.
Do I need to correct my gravity readings for temperature?
Yes. Hydrometers are calibrated to a specific temperature, usually 20 degrees Celsius, and readings taken warmer or cooler read low or high. Correct both your original and final gravity to the calibration temperature before entering them, otherwise the resulting ABV can be off by several tenths of a percent.