Our Specific Gravity to ABV Calculator converts original gravity (OG) and final gravity (FG) hydrometer readings to alcohol by volume (ABV%) — the essential tool for every homebrewer, craft beer maker, and winemaker.
Specific Gravity to ABV Calculator
ABV Formulas Explained
Standard Formula (most used):
ABV = (OG − FG) × 131.25
Alternate Formula (accurate for ABV > 8%):
ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)
Example: OG = 1.050, FG = 1.010
ABV = (1.050 − 1.010) × 131.25 = 5.25%
How to Read Specific Gravity
- Use a hydrometer or refractometer
- Take the OG reading before pitching yeast (start of fermentation)
- Take the FG reading after fermentation is complete (stable for 2–3 days)
- Enter both values in the calculator above
Typical OG and FG Values by Beer Style
| Style | OG Range | FG Range | Typical ABV |
|---|---|---|---|
| Light Lager | 1.028–1.040 | 1.004–1.008 | 3–4% |
| American Pale Ale | 1.045–1.060 | 1.008–1.015 | 4.5–6% |
| IPA | 1.056–1.075 | 1.008–1.018 | 6–7.5% |
| Stout | 1.044–1.060 | 1.010–1.018 | 4–6% |
| Barleywine | 1.080–1.120 | 1.016–1.030 | 8–12% |
What is Apparent Attenuation?
Apparent attenuation measures how much of the original sugar your yeast consumed: AA% = (OG − FG) / (OG − 1) × 100. Most ale yeasts attenuate 73–80%. A high FG (low attenuation) means residual sweetness; a low FG means a dry, thin beer.
Comparing the Two Formulas
The simple formula is a linear approximation and drifts high on strong beers. The alternate formula corrects for that.
| OG | FG | Simple formula | Alternate formula | Difference |
|---|---|---|---|---|
| 1.050 | 1.010 | 5.25 percent | 5.30 percent | Negligible |
| 1.070 | 1.014 | 7.35 percent | 7.55 percent | 0.2 points |
| 1.100 | 1.020 | 10.50 percent | 11.10 percent | 0.6 points |
Below about 8 percent the two agree closely enough that it does not matter. Above that, use the alternate formula for anything you intend to label.
Temperature Correction for Hydrometers
Hydrometers are calibrated at a specific temperature, usually 60 F (15.6 C) or 20 C depending on the instrument. Reading a warm sample gives a falsely low gravity, because warm liquid is less dense.
| Sample temperature | Correction to add |
|---|---|
| 20 C / 68 F | +0.001 |
| 25 C / 77 F | +0.002 |
| 30 C / 86 F | +0.003 to +0.004 |
| 38 C / 100 F | +0.006 to +0.007 |
An uncorrected OG reading taken on hot wort can be several points low, which then understates your final ABV. Cool the sample or apply the correction.
Why a Refractometer Reads Wrong After Fermentation
Refractometers are excellent for pre-fermentation readings and need only a couple of drops. Once alcohol is present, though, they become unreliable, because ethanol bends light differently from sugar.
Attenuation and Stuck Fermentations
If your final gravity is higher than expected, work through these before assuming the yeast has failed:
- Is it actually finished? Take readings on three consecutive days. A stable gravity means fermentation is complete, even if the number is higher than your recipe predicted.
- Was the mash too hot? Mashing above about 68 C produces more unfermentable dextrins, raising final gravity legitimately.
- Temperature drop? Yeast flocculates early if the fermentation gets cold. Gently warming and rousing often restarts it.
- Underpitched or unhealthy yeast? Large or high-gravity batches need a proportionally larger pitch and adequate oxygen at the start.
Most ale yeasts attenuate 73 to 80 percent. A strain at the bottom of its range on a high-gravity wort will leave a noticeably sweet beer without anything having gone wrong.
Common ABV Calculation Mistakes
- Using the simple formula on a strong beer. It understates ABV by up to 0.6 points above 10 percent.
- Not correcting hydrometer temperature. A hot OG reading quietly reduces your calculated ABV.
- Trusting a refractometer for final gravity. It reads high once alcohol is present unless corrected.
- Forgetting priming sugar. Bottle conditioning adds roughly 0.3 to 0.5 percent to the final ABV.
- Reading the wrong part of the meniscus. Read at the level of the liquid surface, not the top of the curve climbing the stem.
Frequently Asked Questions
How do I calculate ABV from OG and FG?
The standard formula is ABV = (OG – FG) x 131.25. For an original gravity of 1.050 and a final gravity of 1.010 that gives (1.050 – 1.010) x 131.25 = 5.25 percent. Above about 8 percent, use the alternate formula instead, since the simple one increasingly understates the result.
Which ABV formula should I use?
Use the simple formula for anything under about 8 percent, where the two methods agree closely. Above that, use the alternate formula: at OG 1.100 and FG 1.020 the simple formula gives 10.5 percent while the alternate gives 11.1 percent, a difference of 0.6 points that matters if you are labelling the beer.
What is specific gravity in brewing?
It measures the density of your wort relative to water, which has a gravity of 1.000. Dissolved sugar raises the gravity, and as yeast converts that sugar into alcohol, which is less dense than water, the gravity falls. The difference between the starting and finishing readings is what tells you how much alcohol was produced.
Do I need to correct my hydrometer reading for temperature?
Yes, unless the sample is at the hydrometer’s calibration temperature, usually 60 F or 20 C. A warm sample reads falsely low because warm liquid is less dense. At 30 C you need to add about 0.003 to 0.004, and at 38 C about 0.006 to 0.007. An uncorrected hot OG reading understates your final ABV.
Can I use a refractometer instead of a hydrometer?
For pre-fermentation readings, yes, and it is more convenient since it needs only a couple of drops. After fermentation begins it becomes unreliable, because ethanol bends light differently from sugar and the instrument reads high. Use a hydrometer for final gravity, or apply a refractometer correction formula that accounts for both readings.
What is a good final gravity for beer?
It depends on style, but 1.008 to 1.015 covers most ales. Light lagers finish lower, around 1.004 to 1.008, while stouts and barleywines finish higher at 1.010 to 1.030. What matters more than the absolute number is whether the gravity has been stable for three consecutive days, which means fermentation is genuinely complete.
Why is my final gravity higher than expected?
Common causes are a mash temperature above about 68 C, which creates more unfermentable dextrins, a fermentation that got too cold and caused the yeast to flocculate early, or an underpitch on a high-gravity wort. First confirm it is actually stuck by taking readings on three consecutive days, since a stable high gravity may simply be a legitimately less fermentable wort.