📋

Walk-through

How to Use This Calculator

4 steps

1

Enter Original Gravity

Take an OG reading with a hydrometer or refractometer right after mixing your wort or must, before pitching yeast, and enter it here (e.g. 1.050).

2

Enter Final Gravity

Once fermentation has fully stopped — a stable reading held over 2-3 days — take an FG reading and enter it (e.g. 1.010).

3

Pick a Formula

Use Standard for most everyday beers, ciders, and meads. Switch to Alternate for high-gravity brews (roughly above 1.070 OG), where the standard linear formula tends to under-report ABV.

4

Check Attenuation and Calories

Switch to the Attenuation tab to see how much of the available extract fermented out, and the Calories tab for an estimated calorie count per 12 fl oz serving.

⚡

Reference

Formula & Methodology

2 formulas

Standard ABV Formula

ABV% = (OG − FG) × 131.25

The most widely used home-brewing ABV formula. Subtract final gravity from original gravity, then multiply by 131.25. Accurate for most beers, ciders, and meads under about 1.070 OG. Example: OG 1.050, FG 1.010 → (1.050 − 1.010) × 131.25 = 5.25% ABV, expressed here as a percentage — see our <a href="../../../math-science/general-math/percentage/">Percentage Calculator</a> for the general percent-change math behind it.

Attenuation

Attenuation% = (OG − FG) / (OG − 1) × 100

Apparent attenuation measures how much of the extract in the original wort fermented into alcohol and CO2, expressed as a percentage of gravity points. Most ale yeasts finish between 72-80% apparent attenuation.

📖

Glossary

Key Terms Explained

7 terms

ABV Alcohol By Volume — the percentage of a beverage's total volume that is pure ethanol. A beer labeled 5% ABV contains 5 ml of alcohol per 100 ml of liquid.

Original Gravity The specific gravity of wort or must measured before fermentation begins, reflecting the amount of fermentable and unfermentable sugar dissolved in the liquid. Typical beer OG ranges from 1.040 to 1.090.

Final Gravity The specific gravity measured after fermentation is complete, once yeast has consumed the fermentable sugars. A lower FG generally means a drier finish and higher alcohol content.

Attenuation The percentage of extract converted by yeast during fermentation, calculated from the drop in gravity from OG to FG. Apparent attenuation is the commonly quoted figure; real attenuation accounts for alcohol's effect on the hydrometer reading and is always a few points lower.

Specific Gravity The density of a liquid relative to water at a reference temperature, where pure water equals 1.000 — see our <a href="../../../science/matter-waves/density/">Density Calculator</a> for the underlying density math. Brewers use specific gravity readings before and after fermentation to track sugar conversion and estimate alcohol content.

Fermentation The biological process by which yeast metabolizes sugars into ethanol and carbon dioxide. Fermentation typically runs 1-3 weeks for beer, with gravity readings used to confirm when it has finished.

Brix A measurement of dissolved sugar content in a liquid, expressed in degrees, commonly used in winemaking and juice production. One degree Brix is roughly equivalent to 4 gravity points (0.004 specific gravity) at typical must concentrations.

👥

Scenarios

Real-World Examples

3 worked examples

🍺

Dan

Standard Pale Ale

Original Gravity 1.050 Final Gravity 1.010 Formula Standard

Dan's pale ale drops from 1.050 to 1.010, giving (1.050 − 1.010) × 131.25 = 5.25% ABV with 80% apparent attenuation — a clean, fully-fermented result typical of an American ale yeast.

🍷

Priya

High-Gravity Barleywine

Original Gravity 1.095 Final Gravity 1.022 Formula Alternate

At 1.095 OG the standard formula would read about 9.59% ABV, but the Alternate high-gravity formula corrects for yeast stress and alcohol's effect on gravity readings, giving a more accurate estimate near 9.8% ABV for this big barleywine.

🍏

Maria

Dry Cider

Original Gravity 1.055 Final Gravity 1.000 Formula Standard

Maria's cider ferments all the way down to 1.000 — essentially bone dry — giving (1.055 − 1.000) × 131.25 = 7.22% ABV and 100% apparent attenuation, the mark of a fully fermented cider with no residual sweetness.

📄

Deep Dive

Understanding ABV, Attenuation, and Calories in Home Brewing

4 chapters · 4 min read

Alcohol by volume is the single most-asked-about number in home brewing, and it comes entirely from two hydrometer readings: original gravity and final gravity. This guide explains how the ABV formula works, why an alternate formula exists for stronger brews, what attenuation tells you about your yeast, and how brewers estimate the calories in a finished beer. If you're stocking drinks for an event rather than brewing them, our Drinks for a Party Calculator and Wine Bottle Calculator figure out quantities instead; for tracking consumption in your body rather than in the fermenter, see our Blood Alcohol (BAC) Calculator and Alcohol Units Calculator.

Why Two Gravity Readings Are Enough

Specific gravity measures dissolved sugar (and other solids) in your wort or must relative to water. Before fermentation, that sugar is almost entirely fermentable extract; after fermentation, most of it has been converted to alcohol and CO2, which lowers the density of the liquid. The drop in gravity from OG to FG is therefore a reliable proxy for how much sugar became alcohol, which is why the standard formula — (OG − FG) × 131.25 — only needs those two numbers to produce a usable ABV estimate.

Standard vs. Alternate Formula

The standard linear formula assumes a roughly constant relationship between gravity drop and alcohol produced. That assumption holds well for typical beers under about 1.070 OG, but it increasingly under-reports ABV as starting gravity climbs, because higher-alcohol fermentations produce proportionally more alcohol per gravity point consumed. The alternate (high-gravity) formula — 76.08 × (OG − FG) / (1.775 − OG) × (FG / 0.794) — corrects for this non-linearity and is the formula most homebrew software defaults to for barleywines, imperial stouts, and other big beers.

Reading Attenuation

Apparent attenuation — (OG − FG) / (OG − 1) × 100 — tells you what fraction of the wort's extract fermented out. Most ale yeasts land between 72% and 80% apparent attenuation; some Belgian and saison strains push past 85-90%. A lower-than-expected attenuation usually signals an unfinished fermentation, an underpitched or stressed yeast, or a mash that produced too many unfermentable dextrins; a much higher-than-expected number can indicate a stuck hydrometer reading, a contamination issue, or the use of highly fermentable adjuncts like table sugar.

Estimating Calories

Homebrew calorie estimates commonly use the Real Extract method (M.L. Hall, "Brew By the Numbers," Zymurgy, Summer 1995), which converts OG and FG into degrees Plato, derives the real extract remaining in the beer, and combines it with the alcohol-by-weight percentage to estimate total calories per serving. This is an approximation — it does not account for unfermentable adjuncts like lactose or maltodextrin added after the boil — but it lines up closely with the calorie counts published by major commercial breweries for beers of similar OG, FG, and ABV.

❓

Questions

Frequently Asked Questions

6 questions

What formula does this calculator use?+

The Standard formula is ABV% = (OG − FG) × 131.25. For example, an original gravity of 1.050 and a final gravity of 1.010 gives (1.050 − 1.010) × 131.25 = 5.25% ABV. An Alternate high-gravity formula is also available for beers above roughly 1.070 OG.

What is original and final gravity?+

Original gravity (OG) is the specific gravity of your wort or must measured before fermentation, and final gravity (FG) is the specific gravity measured once fermentation is complete. Both are measured with a hydrometer or refractometer, with pure water reading 1.000.

What is attenuation and what's a normal range?+

Attenuation is the percentage of extract that fermented out, calculated as (OG − FG) / (OG − 1) × 100. Most ale yeasts finish between 72% and 80% apparent attenuation; a much lower number can mean fermentation isn't finished yet.

How accurate is the calorie estimate?+

The calorie estimate uses the widely cited Real Extract method, which derives real extract and alcohol-by-weight from your OG and FG readings. It's a solid approximation for beers, ciders, and meads made from fermentable sugars, but it won't account for unfermentable additions like lactose, maltodextrin, or fruit purée added after fermentation.

How do I convert a Brix reading to gravity?+

As a rough rule of thumb, 1 degree Brix is approximately equal to 4 gravity points (0.004 specific gravity) in typical must concentrations, so a 22 Brix must is roughly 1.088 OG. For precision work, use a full Brix-to-SG conversion table, since the relationship is not perfectly linear across the full range.

Why might my actual ABV differ from this estimate?+

Hydrometer readings are temperature-sensitive and need correction if taken far from the calibration temperature (usually 60°F/15.6°C or 68°F/20°C); readings can also be thrown off by trapped CO2, a dirty or uncalibrated hydrometer, or measuring before fermentation has fully finished. This calculator provides an estimate for home-brewing purposes, not a laboratory-grade alcohol measurement.

Download a one-page PDF of your numbers instantly. Add your email to also get our occasional calculator tips — no spam, unsubscribe anytime. Privacy.

ABV Calculator

Inputs

Result

Apparent Attenuation

Estimated Calories (per 12 fl oz)

How to Use This Calculator

Enter Original Gravity

Enter Final Gravity

Pick a Formula

Check Attenuation and Calories

Formula & Methodology

Key Terms Explained

Real-World Examples

Dan

Priya

Maria

Understanding ABV, Attenuation, and Calories in Home Brewing

Why Two Gravity Readings Are Enough

Standard vs. Alternate Formula

Reading Attenuation

Estimating Calories

Frequently Asked Questions

Get a branded PDF of your results

ABV Calculator

Inputs

Result

Apparent Attenuation

Estimated Calories (per 12 fl oz)

How to Use This Calculator

Enter Original Gravity

Enter Final Gravity

Pick a Formula

Check Attenuation and Calories

Formula & Methodology

Key Terms Explained

Real-World Examples

Understanding ABV, Attenuation, and Calories in Home Brewing

Why Two Gravity Readings Are Enough

Standard vs. Alternate Formula

Reading Attenuation

Estimating Calories

Frequently Asked Questions

Get a branded PDF of your results

Keep Exploring

Related calculators

Guides & articles