Free Homebrew ABV Calculator
Calculate alcohol by volume from original and final gravity readings.
What is a homebrew ABV calculator?
A homebrew ABV calculator is a free online tool that helps you calculate alcohol by volume (ABV) for homebrew beer, wine, or cider from original and final gravity readings. It runs entirely in your browser — no signup, no app, and no data is ever sent to a server.
A homebrew ABV calculator converts your hydrometer readings into alcohol percentage. The classic formula is (OG − FG) × 131.25, which works well for beers up to about 6% ABV. For stronger beers, the alternate formula (76.08 × (OG−FG)) ÷ (1.775 − OG) is more accurate because it accounts for the non-linear relationship between gravity and alcohol content at higher concentrations.
How it works
Enter your original gravity (the reading before fermentation) and final gravity (after fermentation). The calculator subtracts FG from OG to get the gravity drop, then applies the standard equation. For beers with a gravity drop of 0.060 or more, it automatically switches to the high-gravity formula. It also shows your attenuation percentage (how much of the fermentable sugar the yeast consumed) and approximate calories per 12 oz serving.
When to use a homebrew ABV calculator
Every time you bottle or keg a batch of homebrew. Knowing the exact ABV is essential for labeling, especially if you're sharing with friends or entering competitions. The calculator also helps you dial in recipes — if your actual ABV is consistently lower than planned, you may need to adjust your mash temperature, grain bill, or yeast selection.
Common mistakes with ABV calculation
The most common mistake I see homebrewers make is taking hydrometer readings at the wrong temperature. Hydrometers are calibrated at 60°F (15.6°C). If you take a reading at 80°F, your gravity will read about 0.002 lower than actual — that translates to roughly 0.25% ABV error. Always let your sample cool to calibration temperature or use an online correction. The calculator assumes your readings are temperature-corrected, so make sure they are.
Another frequent error is using the standard formula ABV = (OG − FG) × 131.25 for high-gravity beers. This formula loses accuracy above about 1.060 OG because the relationship between gravity drop and alcohol isn't perfectly linear. A beer with OG 1.090 and FG 1.020 gives 9.2% using the standard formula, but the alternative high-gravity formula gives about 9.5% — close to a half-percent difference. The calculator auto-selects the correct formula based on your gravity readings.
I also find that brewers don't account for additional fermentables added after the OG reading. If you dry-hop with sugar, add honey, or krausen with additional wort, your actual alcohol will be higher than the OG-to-FG calculation shows. For the most accurate ABV, take a new gravity reading after any fermentable addition. The calculator gives you the ABV for whatever OG and FG pair you enter, so you can track stepwise additions.
How to use this calculator
- Enter original gravity — Input your OG reading from before fermentation began.
- Enter final gravity — Input your FG reading after fermentation is complete.
- Get your ABV — Alcohol percentage appears instantly, along with approximate calories.
Frequently asked questions
How do I calculate ABV from OG and FG?
ABV = (OG − FG) × 131.25. For a beer with OG 1.050 and FG 1.010: (1.050 − 1.010) × 131.25 = 5.25% ABV. For higher-gravity beers (over 6%), use the alternate formula ABV = (76.08 × (OG−FG)) ÷ (1.775 − OG) for better accuracy.
What is a good OG for homebrew beer?
OG depends on the style. Light beers: 1.030-1.040 (3-4% ABV). Standard ales and lagers: 1.040-1.060 (4-6% ABV). Strong ales, IPAs, stouts: 1.060-1.080 (6-9% ABV). Imperial stouts and barleywines: 1.080-1.120+ (9-14% ABV). The calculator works for any OG range.
How do I measure OG and FG?
Use a hydrometer or refractometer. Take a reading before pitching yeast (OG) and another after fermentation is complete (FG). For hydrometers, read the specific gravity at the bottom of the meniscus at 60°F. For refractometers, use a wort correction calculator after fermentation because alcohol distorts the reading.
What if my FG is higher than expected?
A higher-than-expected FG means fermentation stopped early — either from a stuck fermentation, low yeast health, or too-cold temperatures. The ABV will be lower than planned. Common fixes: raise the temperature, re-pitch yeast, or add yeast nutrient. The calculator still gives the accurate ABV for whatever gravity you actually reached.
How do I calculate ABV for wine or cider?
The same ABV formula works for wine and cider: ABV = (OG − FG) × 131.25. Wine typically has OG 1.080-1.120 and ferments to FG 0.990-1.010, giving 9-14% ABV. Cider has OG 1.040-1.070 and FG 1.000-1.020, giving 3-7% ABV. The auto high-gravity formula switch also applies to wine with OG above 1.070.
What is attenuation and why does it matter?
Attenuation is the percentage of fermentable sugars the yeast consumed, calculated as (OG − FG) ÷ (OG − 1) × 100. A beer with OG 1.050 and FG 1.012 has 76% attenuation. Low attenuation (under 70%) leaves residual sweetness. High attenuation (over 80%) produces a drier, crisper finish. Yeast strain and mash temperature are the biggest factors controlling attenuation.