# ABV Calculator (Alcohol By Volume)

Calculate alcohol by volume (ABV) from original and final gravity readings for homebrewing. See ABV, attenuation, and estimated calories per pint.

## What this calculates

Wondering how strong your homebrew turned out? Enter your original gravity (before fermentation) and final gravity (after fermentation) to calculate the alcohol content, attenuation, and estimated calories.

## Inputs

- **Original Gravity (OG)** — min 1, max 1.2 — Gravity reading before fermentation (e.g., 1.050)
- **Final Gravity (FG)** — min 0.99, max 1.1 — Gravity reading after fermentation (e.g., 1.010)

## Outputs

- **Alcohol By Volume (ABV)** — Estimated alcohol content by volume
- **Alcohol By Weight (ABW)** — Alcohol content by weight (ABV x 0.79)
- **Apparent Attenuation** — Percentage of sugars converted to alcohol and CO2
- **Estimated Calories (per pint)** — Approximate calories per 16 oz pint

## Details

The standard ABV formula used by homebrewers is: **ABV = (OG - FG) x 131.25**. This takes the difference between your original gravity (OG) and final gravity (FG) and converts it to a percentage of alcohol by volume.

For example, a beer with an OG of 1.050 and FG of 1.010 has an ABV of (1.050 - 1.010) x 131.25 = 5.25%. That puts it right in the range of a typical American pale ale.

Apparent attenuation tells you what percentage of the original sugars the yeast converted. Most healthy fermentations hit 70-80% attenuation. Below 65% might mean the fermentation stalled, while above 85% indicates a very dry beer. Different yeast strains have characteristic attenuation ranges -- a Belgian strain might push 85%+ while an English ale yeast might settle around 72%.

The 131.25 constant comes from the mathematical relationship between specific gravity units and the density change caused by ethanol replacing sugar in solution. For very high-gravity beers above 8% ABV, some brewers prefer the more precise alternate formula: ABV = (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794), which accounts for non-linear effects at higher alcohol concentrations.

## Frequently Asked Questions

**Q: How do I measure original and final gravity?**

A: Use a hydrometer or refractometer. For a hydrometer, fill the test jar with a sample of your wort or beer (cooled to the hydrometer's calibration temperature, usually 60F/15.6C), float the hydrometer, and read the scale at the meniscus. Take your OG reading before pitching yeast and your FG reading when fermentation appears complete (stable gravity readings over 2-3 days).

**Q: What is a normal attenuation percentage?**

A: Most ale yeast strains attenuate between 70% and 80%. Lager yeasts typically reach 75-85%. Belgian and saison strains can push 85-95%. If your attenuation is below 65%, the fermentation may have stalled due to temperature issues, insufficient yeast, or low nutrient levels. Check your yeast strain's spec sheet for its expected attenuation range.

**Q: Why is my ABV higher or lower than expected?**

A: Inaccurate gravity readings are the most common cause. Make sure your hydrometer sample is at the correct calibration temperature (usually 60F). Bubbles clinging to the hydrometer can also cause false readings. If using a refractometer for FG, remember that alcohol affects the reading and you need to apply a correction factor. Also verify your recipe's expected OG matches what you actually measured.

**Q: Can I use this for wine and cider too?**

A: Yes, the ABV = (OG - FG) x 131.25 formula works for any fermented beverage. Wine typically starts at a higher OG (1.080-1.120) and finishes very dry (0.990-1.000), producing ABV in the 10-15% range. Cider usually starts around 1.045-1.065 and can finish quite dry, giving 5-8% ABV. The formula is the same regardless of the base sugar source.

---

Source: https://vastcalc.com/calculators/health/alcohol-by-volume
Category: Health & Fitness
Last updated: 2026-04-08