ABV Calculator
Enter original gravity and final gravity to get the alcohol by volume.
What this tool does
Homebrewers estimate alcohol by volume from two hydrometer readings: ABV = (OG − FG) × 131.25. An original gravity of 1.050 and a final gravity of 1.010 gives 0.040 × 131.25 = 5.25% ABV, with 80% apparent attenuation. Enter your readings above.
Applies the standard (OG − FG) × 131.25 formula and a more exact alternative.
Reports the apparent attenuation, the share of sugars the yeast used.
How to use it
- Measure the original gravity before fermentation.
- Measure the final gravity when it is finished.
- Enter both.
- Read the ABV and attenuation.
Why use this calculator
Converts the original and final gravity readings from a hydrometer into ABV with both the common homebrew formula and a more exact formula for stronger brews, plus the apparent attenuation. A hydrometer reading is just a number, and the ABV is what you actually want to know. The standard formula is simple, but a second formula is more accurate for strong beers and wines.
Why we built it
We built the ABV calculator to give two formulas and the apparent attenuation, and to reject readings that cannot be right. Convert volumes with the litres to gallons converter and tweak recipes with the recipe scaler.
Who this tool is for
- Homebrewers measuring fermentation
- Cider and mead makers
- Students learning hydrometer readings
When to use it
- Brewing beer, cider or mead at home.
- Checking that fermentation is finished.
- Comparing batches.
- Labelling homemade drinks for your own use.
How it works
The common estimate is ABV = (OG − FG) × 131.25. A more exact version is ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794), which tracks strong brews better. Apparent attenuation = (OG − FG) ÷ (OG − 1).
Example: OG 1.050, FG 1.010: simple 5.25%, more exact 5.34%, attenuation 80%.
Take readings at the temperature your hydrometer is calibrated for, or correct them. Laws on home brewing, labelling and selling differ by country.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Original gravity | 1.05 |
| Final gravity | 1.01 |
With those inputs, the calculator returns:
- ABV (standard formula): 5.25%
- ABV (more exact for strong beers): 5.34%
- Apparent attenuation: 80.0%
- Original gravity in °Plato (approx.): 12.4
What you give it, and what you get back
| Item | Details |
|---|---|
| Original gravity (OG) | Reading before fermentation, e.g. 1.050. |
| Final gravity (FG) | Reading after, e.g. 1.010. |
| Output | ABV (two formulas), apparent attenuation and the original gravity in °Plato. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| "FG higher than OG" error | The readings are swapped or wrong. | Re-measure. |
| ABV looks off | The sample was warm or not degassed. | Cool and degas the sample. |
| Very high gravity beer | The simple formula drifts. | Use the second figure. |
Assumptions and limitations
- Estimates from hydrometer readings.
- Does not include added sugars measured separately.
Frequently asked questions
How do I calculate ABV?
Subtract the final gravity from the original and multiply by 131.25.
What is original gravity?
The density of the unfermented liquid, which shows how much sugar it holds.
What is a typical final gravity?
Often 1.008-1.016 for beer.
What is attenuation?
The share of sugars the yeast converted.
Is the formula exact?
It is an estimate; it is accurate enough for most beers.
Is my information sent anywhere?
No. The calculation runs in your browser and nothing leaves the page.
Sources and accuracy
Alcohol by volume is estimated from the change in specific gravity between original and final readings using the standard brewing relationship ABV equals original gravity minus final gravity, times 131.25. Alcohol content measurement and labeling are regulated by the Alcohol and Tobacco Tax and Trade Bureau.
- Alcohol and Tobacco Tax and Trade Bureau - Alcohol
- NIST Guide to the SI, Appendix B Conversion Factors
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.