Beer ABV Calculator
Estimate beer ABV (alcohol by volume) from Original Gravity and Final Gravity. Simple and alternate formulas side by side, HMRC factor-table cross-check, Balling model on a curved Plato scale, apparent attenuation, degrees Plato and a calorie estimate.
Beer ABV Calculator
Enter Original Gravity (OG, e.g. 1.050) and Final Gravity (FG, e.g. 1.010). OG must exceed FG.
How to use the Beer ABV Calculator
Take the original gravity before the yeast goes in
OG (Original Gravity) is the specific gravity of the wort just before yeast is added. Read it with a hydrometer in a sample jar, at the temperature the instrument is calibrated for (printed on the hydrometer or in its paperwork), or correct the reading with the maker's chart. For the OG range a style is expected to start from, look the style up in the BJCP Style Guidelines, which give OG, FG and ABV ranges for each one.
Take the final gravity once the readings stop changing
FG (Final Gravity) is the specific gravity after fermentation has finished, which shows as readings taken on different days no longer changing. A refractometer reading taken now is skewed by the alcohol (see the refractometer question below), so use a hydrometer here or a correction that takes both readings. The BJCP guidelines also give an FG range for each style.
Read both ABV estimates side by side
The simple rule is ABV = (OG − FG) × 131.25. The alternate formula is 76.08 × (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794, which brewing calculators attribute to Michael Hall's 1995 Zymurgy article. Neither is a laboratory measurement, and the page does not rank them. They drift apart as gravity rises: on this calculator's arithmetic the alternate reads 0.09 points higher at OG 1.050 / FG 1.010, 0.21 at 1.060 / 1.012, 0.37 at 1.070 / 1.015, 0.56 at 1.080 / 1.018 and 1.07 at 1.100 / 1.025. Underneath, HMRC's factor table gives an outside figure for the same readings, and the Balling model shows what the alternate's own method gives on a curved sugar scale.
Compare attenuation with your yeast's spec sheet
Apparent attenuation = (OG − FG) ÷ (OG − 1): the share of the original gravity that fermentation removed. What counts as normal depends on the strain, and the yeast makers (Wyeast, White Labs, Fermentis, Lallemand) list an expected range on each strain's spec sheet. If your figure is well below that range, the maker's guidance is the place to start.
Brewing math — how OG, FG, and gravity readings actually work
Specific Gravity (SG) compares the density of a liquid with pure water (1.000). Wort is denser than water because of the extract dissolved from the malt. During fermentation that extract is used up: MEBAK, the German brewing-analysis commission, states Balling's mass balance as "1 g of alcohol, 0.9565 g of carbon dioxide and 0.11 g of yeast are produced on average from 2.0665 g of extract". Alcohol is less dense than water and most of the carbon dioxide leaves, so the gravity drops. The drop from Original Gravity to Final Gravity is what every formula on this page turns into an alcohol figure.
Why the two formulas give different answers
Neither constant comes with a source we could open: 131.25 and the alternate's 76.08, 1.775 and 0.794 appear on brewing calculators without a primary reference we could check. A tax authority publishes its own version of the job. HMRC's Alcoholic products technical guide (§11.8) gives brewers "with no or minimal laboratory facilities" the method "(original gravity – present gravity) × f = a% alcohol by volume", with gravity in UK degrees (1040 for SG 1.040), and a factor table produced by the Laboratory of the Government Chemist in which f rises from 0.125 for the smallest gravity drops to 0.135 for the largest. HMRC gives the reason: "in lower strength beer, more of the 'sugars' available for fermentation are consumed in yeast reproduction than in producing alcohol". On that scale the simple rule's 131.25 is 0.13125 per degree, between the table's 0.131 and 0.132 factors; HMRC puts most popular UK beers at 0.129 to 0.130.
We set both formulas beside HMRC's factor table, the one external reference we could check, and beside a fourth figure that is not independent: Balling's relation as MEBAK states it, with the real-extract split brewing calculators use (0.1808 × OG °P + 0.8192 × FG °P, which is not in MEBAK's abstract) and this calculator's curved SG-to-Plato scale. As the next paragraphs show, that is the alternate formula's own model with a different sugar scale. At 75% apparent attenuation:
| OG / FG | Simple rule | Alternate | Balling model, curved scale | HMRC factor |
|---|---|---|---|---|
| 1.030 / 1.008 | 2.89% | 2.85% | 2.90% | 2.82% |
| 1.050 / 1.012 | 4.99% | 5.08% | 5.05% | 4.94% |
| 1.070 / 1.018 | 6.83% | 7.19% | 6.98% | 6.81% |
| 1.080 / 1.020 | 7.88% | 8.44% | 8.09% | 7.92% |
| 1.090 / 1.022 | 8.93% | 9.72% | 9.22% | 9.04% |
| 1.100 / 1.025 | 9.84% | 10.91% | 10.22% | 9.98% |
| 1.120 / 1.030 | 11.81% | 13.56% | 12.38% | 12.15% |
Up to an OG of about 1.055 all four stay within a quarter of a point of each other. From about 1.060 the alternate reads higher than the other three, and the gap grows with gravity. Across every case we checked (OG 1.030 to 1.120, apparent attenuation 60 to 90%), HMRC's factors stayed within 0.37 points of the simple rule, sometimes above it and sometimes below, while the alternate read up to 1.47 points above them. That is a statement about distance, not accuracy: without a laboratory result, none of the four can be called right.
The alternate's constants are what you get if you take Balling's relation with that split and replace the curved SG-to-Plato scale with the straight line °P ≈ 250 × (SG − 1): the algebra gives 76.81 and 1.7751, against the published 76.08 and 1.775. So the Balling column and the alternate share one model and differ in the sugar scale (and that constant). The straight line reads Plato higher as gravity rises: at SG 1.100 it gives 25.0 °P, against 23.77 °P on the curve this calculator uses. Whether that is how the formula was first derived we cannot say; the original article was not available to us.
A gravity estimate is not the figure a label or a duty return refers to. HMRC's guide says strength for duty is measured at 20°C and that its factor table "is primarily for your guidance".
Attenuation — what the yeast removed
Apparent attenuation = (OG − FG) ÷ (OG − 1), as a percentage. It is called apparent because the alcohol in the finished beer is lighter than water, so the FG reads lower than the extract actually left behind. That is why it can pass 100%: OG 1.040 with FG 0.998 gives 105.0%. This calculator estimates the extract actually left (the real extract) with the 0.1808 / 0.8192 split above, and refuses readings that would leave less than none, because no fermentation can use up more extract than the wort held. To judge your figure, compare it with the range the yeast maker lists for the strain.
The ASEAN homebrew + craft beer angle
Singapore sets its home-brewing rules out plainly. Under the Customs (Home-Brewing of Fermented Liquors) (Exemption) Order, in force since 2008, you need no licence to brew at home if you are 18 or older, ferment rather than distil, make no more than 30 litres of beer per household per month (and no more than 30 litres in total of other fermented liquors), brew in your own home, keep it for personal use rather than sale, and cause no nuisance. Singapore Customs publishes these conditions on its website. Duty on liquor is charged on strength: Singapore Customs gives the formula as total quantity in litres × duty rate × percentage of alcoholic strength, which is one more reason a homebrew estimate is not a declared strength. Elsewhere in the region the rules differ from country to country and do change, so check your own country's current law before you brew.
From gravity drop to alcohol: 131.25, HMRC's factor table and Balling's mass balance
The simple rule's 131.25 is 0.13125 per degree of gravity drop, between the 0.131 and 0.132 factors of HMRC's table. HMRC puts most popular UK beers at 0.129 to 0.130.
HMRC's factor rises with strength, from 0.125 to 0.135, because in weaker beer more of the sugar goes into yeast reproduction rather than alcohol.
On this calculator's arithmetic the alternate formula reads 0.56 points above the simple rule at OG 1.080 / FG 1.020, and 1.07 points above at 1.100 / 1.025, where HMRC's factor table gives 9.98%.
Balling's mass balance, as MEBAK states it: on average 2.0665 g of extract gives 1 g of alcohol, 0.9565 g of carbon dioxide and 0.11 g of yeast.
The Plato scale expresses extract as percent by mass. On the cubic this calculator uses, SG 1.048 converts to 11.91 °P and SG 1.100 to 23.77 °P.
Hydrometers read density by buoyancy, and a warmer sample is less dense, so it reads low. Calibration temperatures differ between instruments: read at the one printed on yours, or use its correction chart.
A refractometer reading depends on more than sugar. MEBAK: refraction "is a function of concentration (alcohol/extract), temperature and wavelength", so after fermentation it needs a correction that also uses the original reading.
In Singapore you can home-brew without a licence up to 30 litres of beer per household per month, if you are 18 or over and it is for personal use (Customs exemption order, 2008).
The BJCP Style Guidelines give an OG, FG and ABV range for every beer style: the quickest check on whether your readings fit the beer you meant to brew.
Energy comes from alcohol plus the extract left in the beer. By the formula this calculator uses, OG 1.050 / FG 1.010 comes to about 46 kcal per 100 mL, and OG 1.080 / FG 1.020 to about 74. An estimate from gravity readings, not a nutrition analysis.
Frequently Asked Questions
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OG (Original Gravity) is the specific gravity of wort BEFORE fermentation, which reflects how much extract is dissolved in it. FG (Final Gravity) is the specific gravity AFTER fermentation, once the yeast has used what it can. The drop from OG to FG is what the formulas turn into alcohol. Take both readings with a hydrometer floating in a sample at the temperature the instrument is calibrated for, which differs between instruments; a refractometer reads a few drops instead, and needs a correction for the FG reading.
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We cannot tell you, and neither formula comes with a source that settles it. What we can measure is how far apart they are and where an outside reference lands. On this calculator's arithmetic the alternate reads 0.09 ABV points above the simple rule at OG 1.050 / FG 1.010 and 0.21 at 1.060 / 1.012, widening to 0.56 at 1.080 / 1.018 and 1.07 at 1.100 / 1.025. The one external reference we could check, HMRC's factor table, stayed within 0.37 points of the simple rule, either side of it, in every case we checked, while the alternate read up to 1.47 points above it. None of these is a laboratory measurement, and none is a figure for a label or a duty return: the method in the UK regulations HMRC quotes distils a sample at 20°C and measures the distillate's density with a pycnometer.
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It depends on the yeast strain, and the people who know are the yeast makers: Wyeast, White Labs, Fermentis and Lallemand list an expected attenuation range on each strain's spec sheet. Compare your result against that range rather than a general figure. If your attenuation is well below the strain's expected range, fermentation might be stuck.
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"Stuck" means the gravity stopped falling before it reached what the strain normally achieves. First confirm it: take readings on different days at the hydrometer's calibration temperature, and compare the attenuation this calculator shows with the range on the strain's spec sheet. If it really has stopped short, the yeast maker's own guidance for that strain is the place to look; this page does not prescribe a fix.
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Liquid density changes with temperature — warmer liquids are less dense, so the hydrometer floats lower and reads a lower SG. Each hydrometer is calibrated at a stated temperature, and instruments differ, so check the one printed on yours or in its paperwork. For readings at other temperatures, use the correction chart that comes with the instrument; cooling the sample to the calibration temperature avoids the question altogether. This calculator applies no temperature correction, so enter corrected readings.
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Only with a correction for the second reading. MEBAK, the German brewing-analysis commission, describes refraction as "a function of concentration (alcohol/extract), temperature and wavelength", so once alcohol is present the reading no longer reflects extract alone, and a fixed factor will not fix it because the error depends on how much alcohol there is. Use a correction that takes both the original and the current reading, or take the FG with a hydrometer. This calculator takes specific gravity only.
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Specific Gravity (SG) is a density ratio against pure water (1.000), which is what a hydrometer reads. Plato (°P) expresses extract as percent by mass; this calculator converts both of your readings to °P with a cubic fit, so SG 1.048 shows as 11.91 °P. Brix is the scale most refractometers display. This calculator does not take Brix readings and does not convert to or from Brix; enter specific gravity.
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It uses the formula brewing calculators attribute to Michael Hall's 1995 Zymurgy article (the article itself was not available to us), which counts energy from alcohol and from the extract left in the beer. The calculator converts both gravities to degrees Plato, estimates the real extract as 0.1808 × °P(OG) + 0.8192 × °P(FG), and converts the simple-rule ABV to alcohol by weight (ABV × 0.79336 ÷ FG). Energy per 100 mL is then (6.9 × ABW + 4.0 × (real extract − 0.1)) × FG kcal: 6.9 kcal per gram of alcohol and 4 per gram of extract. The serving figure scales that to the size you pick. It is an estimate from gravity readings, not a nutrition analysis.
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No. All calculations run entirely in your browser via JavaScript. There's no server roundtrip — open DevTools → Network and confirm zero outbound requests when you change a reading. Your gravity readings stay on your device.
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It varies by country, so check your own country's current law before you brew. Singapore is the clearest case: under the Customs (Home-Brewing of Fermented Liquors) (Exemption) Order of 2008, no licence is needed if you are 18 or older, ferment rather than distil, make no more than 30 litres of beer per household per month, brew at home, and keep it for personal use, not for sale. Singapore Customs lists the full conditions on its website. The math in this calculator is universal, but always brew within your jurisdiction's rules.
Method & sources
How it computes
ABV from OG and FG two ways, side by side and unranked: (OG − FG) × 131.25, and 76.08 × (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794 (attributed to Hall 1995; original not seen). Cross-check: HMRC’s LGC factor table; also the Balling model (MEBAK) on a curved Plato scale. Apparent attenuation = (OG − FG) ÷ (OG − 1). °Plato by a cubic SG fit; energy by Hall’s formula from the simple-rule ABV. OG outside 1.000–1.200, FG below 0.990 or not below OG, and a negative real extract are refused.
What this tool implements
- Two homebrew formulas reported side by side and not ranked: simple (OG − FG) × 131.25 and alternate 76.08 × (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794. Neither constant has a primary source on file; brewing calculators attribute the alternate to Hall (Zymurgy 1995), and the article was not seen. Until 2026-10-12 the page told readers to trust the alternate for strong beer; no source supported that ranking.
- Balling model, NOT an independent check: Balling’s relation as MEBAK states it (method B-590.10.070: "1 g of alcohol, 0.9565 g of carbon dioxide and 0.11 g of yeast are produced on average from 2.0665 g of extract"), solved for alcohol by mass and converted to ABV with FG ÷ 0.7907. Real extract by the split brewing calculators use, 0.1808 × °P(OG) + 0.8192 × °P(FG); that split is not in the MEBAK abstract. The alternate formula is what this model gives on the straight-line scale °P ≈ 250 × (SG − 1) (constants 76.81 and 1.7751 against the published 76.08 and 1.775), so the two share one model.
- External cross-check: HMRC Alcoholic products technical guide §11.8, (original gravity − present gravity) in degrees × f, with f from the Laboratory of the Government Chemist table (0.125 for drops up to 6.9 degrees, rising to 0.135 for 89.8–100.7). HMRC guidance for brewers with no or minimal laboratory facilities, "primarily for your guidance", not a legal method; drops beyond 100.7 degrees are reported as outside the table.
- Measured by RECATOOLS over OG 1.030–1.120 × apparent attenuation 60–90% (95 cells): all four estimates within 0.25 ABV points up to OG 1.055; HMRC’s factors within 0.37 points of the simple rule, on both sides of it, while the alternate reads up to 1.47 above them. Formula gaps are not compared with label tolerances, which bound a declared strength against a measured one. A statement about distance, not accuracy: no laboratory measurements were compared.
- °Plato = −616.868 + 1111.14·SG − 630.272·SG² + 135.997·SG³, a cubic fit reproduced by brewing calculators (its attribution to an ASBC fit of the de Clerck tables was not verified). Energy per 100 mL = (6.9 × ABW + 4.0 × (RE − 0.1)) × FG, with ABW = simple-rule ABV × 0.79336 ÷ FG; an estimate, not a nutrition analysis.
- Refusals (RECATOOLS limits, stated on the page): OG above 1.000 and at most 1.200; FG from 0.990 to 1.200 and below OG; and a real extract of zero or more (the apparent-attenuation bound). Readings are assumed corrected to the hydrometer’s calibration temperature, which differs between instruments; no temperature correction is applied.
Sources
- MEBAK. Method B-590.10.070: Original gravity extract and alcohol — refractometric method [2025-04] (public abstract; states the Balling relation). https://www.mebak.org/en/methode/b-590-10-070/original-gravity-ex…
- HM Revenue & Customs. Alcoholic products technical guide, Section 11: alcoholic strength (factor table produced by the Laboratory of the Government Chemist). GOV.UK, 2024. https://www.gov.uk/guidance/alcoholic-products-technical-guide/se…
- Beer Judge Certification Program. BJCP Style Guidelines, 2021 edition. https://www.bjcp.org/bjcp-style-guidelines/
- Singapore Customs. Home-Brewed Beer and Other Fermented Liquors — Customs (Home-Brewing of Fermented Liquors) (Exemption) Order (S 194/2008). https://www.customs.gov.sg/know-customs/acts-legislation/customs-…
- Hall ML. Brew by the Numbers: Add Up What’s in Your Beer. Zymurgy 1995;18(2) — as reproduced by brewing calculators; the original article was not seen.
What can make this go out of date
- Singapore home-brewing exemption (30 L per household per month, 18+, fermentation only, personal use) — Customs (Home-Brewing of Fermented Liquors) (Exemption) Order; re-check if the Order is amended
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