How to Calculate ABV of Home Brew Beer and Wine
Quick answer: Take a hydrometer reading before fermentation (original gravity, OG) and another when it has finished (final gravity, FG). Then use ABV = (OG − FG) × 131.25. For example, a beer that starts at 1.050 and finishes at 1.010 is (1.050 − 1.010) × 131.25 = 5.25% ABV.
Yeast turns sugar into alcohol and carbon dioxide. Sugar makes liquid denser and alcohol makes it lighter, so the drop in density between the start and the end of fermentation tells you how much sugar became alcohol. A hydrometer measures that density, which brewers call specific gravity. If you'd rather skip the maths, our free ABV calculator does it for you, but it's worth knowing how it works.
What you need
- A wine and beer hydrometer.
- A trial jar to float it in, so you don't dip anything into the fermenter.
- A thermometer, because temperature changes the reading.
- ChemSan to sanitise everything that touches the brew.
- A notebook or your phone, to write each reading down with the date.
Step 1: take the original gravity (OG)
Once your wort or must is mixed, topped up and stirred, but before you add the yeast, fill a sanitised trial jar. Lower the hydrometer in and give it a gentle spin to knock off any bubbles. Read the scale at the flat surface of the liquid, not the curve that climbs up the stem. Write it down. A typical beer kit starts somewhere around 1.035 to 1.050, and a wine kit is usually higher.
Pour the sample away rather than back in. It's a small loss, and it keeps the risk of infection low.
Step 2: take the final gravity (FG)
Bubbling in the airlock slows down long before fermentation is truly finished, so don't go by the airlock. Take a reading, wait a day, and take another. When you get the same reading on two days in a row, fermentation has finished. That figure is your final gravity, and it's also the sign that it's safe to bottle. Beers usually finish between about 1.008 and 1.015, while dry wines and ciders often finish at 1.000 or below.
Step 3: do the sum
Subtract the FG from the OG, then multiply by 131.25. The answer is your ABV as a percentage.
| Brew | OG | FG | Sum | ABV |
|---|---|---|---|---|
| Session bitter | 1.040 | 1.010 | 0.030 × 131.25 | 3.9% |
| Pale ale | 1.050 | 1.010 | 0.040 × 131.25 | 5.25% |
| Dry cider | 1.050 | 1.000 | 0.050 × 131.25 | 6.6% |
| Wine kit | 1.090 | 0.995 | 0.095 × 131.25 | 12.5% |
These are examples only. Your own readings are what count.
Correct for temperature
Hydrometers are calibrated at one temperature, which is printed on the paper scale inside. A warm sample reads low and a cold one reads high. A degree or two either side makes little difference, but a sample taken straight from a warm fermenter, or hot wort from a boil, can be out by enough to skew your ABV. Either let the sample reach the calibration temperature, or use our hydrometer temperature correction calculator.
Strong wines and meads
The simple formula is accurate enough for beer and cider. It starts to under-read for strong brews, roughly anything over 8 to 10%. For wines and meads, many brewers use this longer version instead:
ABV = (76.08 × (OG − FG) ÷ (1.775 − OG)) × (FG ÷ 0.794)
For the wine kit above (1.090 to 0.995), this gives about 13.2%, compared with 12.5% from the simple formula. Our ABV calculator shows both.
Bottle conditioning adds a little more
If you prime your bottles with sugar or carbonation drops, the yeast ferments that too. At a normal priming rate this adds roughly 0.3 to 0.4% ABV. Our priming sugar calculator helps you get the dose right.
Can I use a refractometer instead?
Yes for the OG: a refractometer needs only a couple of drops, which is handy on brew day. But once alcohol is present it reads wrongly, so a raw refractometer FG will give you the wrong ABV. Either take your FG with a hydrometer, or correct the reading with our refractometer alcohol adjustment tool.
Common mistakes
- Forgetting the OG. Without it you can't calculate ABV accurately. If you used a kit, the instructions often give a typical starting gravity you can use as a rough guide.
- Reading the top of the curve. Read where the flat surface of the liquid meets the scale.
- Bubbles on the hydrometer. CO2 clinging to the stem pushes it up and makes the reading too high. Spin it, or let a fizzy sample stand for a few minutes.
- Bottling on a guess. Bottling before the gravity is stable can over-carbonate the bottles. Always check two days in a row.
Find more kit for checking your brews in our hydrometers and testing equipment range. For a closer look at the instrument itself, read how to use a home brew hydrometer.