Calculate ABV from Original Gravity and Final Gravity
Enter your fermentation readings to estimate alcohol by volume (ABV), apparent attenuation, and an optional batch alcohol total.
What is a gravity alcohol calculator?
A gravity alcohol calculator helps brewers estimate alcohol content using two measurements: original gravity (OG) and final gravity (FG). OG tells you how much dissolved sugar was present before fermentation. FG shows what remains after yeast has consumed fermentable sugars.
The difference between OG and FG reflects how much sugar turned into alcohol and carbon dioxide. This is why gravity readings are one of the fastest and most practical ways to estimate ABV in homebrewing.
How the ABV math works
1) Standard homebrewing formula
The most common equation is:
ABV ≈ (OG − FG) × 131.25
This formula is quick, easy, and accurate enough for many beer styles.
2) Alternate advanced formula
An alternate formula can offer better precision at higher gravities:
ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)
The calculator above gives both values so you can compare.
Why OG and FG matter so much
- Recipe planning: Target ABV starts with target OG.
- Fermentation tracking: A stable FG indicates fermentation is complete.
- Style accuracy: Many beer styles have expected ABV ranges.
- Troubleshooting: Unusually high FG may suggest under-attenuation.
Understanding apparent attenuation
Apparent attenuation estimates how much of the gravity drop occurred during fermentation:
Apparent Attenuation (%) = ((OG − FG) / (OG − 1.000)) × 100
Higher attenuation often means a drier finish. Lower attenuation can mean more body and residual sweetness. Yeast strain, mash temperature, and wort composition all influence this number.
Step-by-step: using this calculator correctly
Take quality measurements
Use a calibrated hydrometer or corrected refractometer readings. Small reading errors can noticeably affect ABV results.
Confirm fermentation is done
Take FG readings across 2-3 days. If gravity is stable, fermentation is likely complete and ABV estimate will be more reliable.
Enter data with three decimals
Readings like 1.058 and 1.011 are preferred over rounded values. Better precision gives better estimates.
Common mistakes to avoid
- Using OG and FG from different temperature conditions without correction.
- Calculating ABV before fermentation is complete.
- Confusing Plato and specific gravity units.
- Entering FG that is higher than OG after fermentation is finished.
Typical ABV ranges by beverage type
- Session beer: 3.0% to 4.5%
- Standard ale/lager: 4.5% to 6.5%
- Strong ale/IPA: 6.5% to 9.0%+
- Cider: 4.0% to 8.0%
- Mead: 8.0% to 14.0%+
- Country wine: often 10.0% to 15.0%
Practical tips for better fermentation outcomes
Control temperature
Yeast performance is highly temperature-sensitive. Stable fermentation temperatures help improve attenuation and reduce off-flavors.
Pitch enough healthy yeast
Under-pitching can stall fermentation and leave FG too high. Starter culture health and oxygen management both matter.
Give it enough time
Rushing bottling or packaging can lead to inaccurate ABV estimates and carbonation issues.
Final note
This gravity alcohol calculator gives a strong ABV estimate for homebrewing and recipe evaluation. If you need legal labeling precision, laboratory analysis is the standard. For most brewers, though, gravity-based ABV calculations are practical, fast, and highly useful for building better beer, cider, mead, and wine batches.