Brewing ABV Calculator

How to use

From hydrometer readings to ABV in seconds. Estimate alcohol content, apparent attenuation and target gravity with optional temperature correction.

Choose ABV Calculator and enter original gravity (OG) and final gravity (FG). The default 1.060 and 1.012 give an estimated 6.30% ABV. Use Target ABV to solve target FG or estimate ABV from a target FG. Hydrometer Correction adjusts one observed reading; the collapsed correction section in ABV mode adjusts both readings. Optional expected readings show neutral differences. Copy Result includes current assumptions; Reset restores default readings and turns correction/comparison off. Refresh clears entries.

Original gravity and final gravity

Specific gravity (SG) compares a liquid’s density with water. OG is the reading before fermentation; FG is the later reading entered for the alcohol estimate. A hydrometer responds to the overall liquid density, not only residual sugar. Accurate calibration, temperature, a clear meniscus reading and freedom from bubbles matter. These calculations use hydrometer SG, not uncorrected refractometer readings after alcohol is present.

ABV formula

Estimated ABV (%) ≈ (OG − FG) × 131.25. This simplified relationship is an approximation, not an exact alcohol analysis across every gravity. Other brewing equations exist and may differ, especially at higher gravities. This version uses one primary estimate with no alternate estimate or statistical confidence interval. FG above OG produces a reading-order warning instead of a normal negative alcohol result.

Gravity points

Gravity points = (SG − 1) × 1000. SG 1.060 is 60 points above water, and 1.012 is 12 points. Gravity drop = (OG − FG) × 1000, so the default drop is 48 points. The visual uses a 0.900–1.300 SG axis with text equivalents; displayed readings have three decimals, while calculations retain unrounded values.

Apparent attenuation

Apparent attenuation (%) = (OG − FG) / (OG − 1) × 100. At 1.060 / 1.012, 0.048 / 0.060 × 100 = 80%. This hydrometer density-based measure differs from real attenuation and fermentation efficiency. OG at or below 1.000 is shown as unavailable because its denominator is zero or unsuitable for this interpretation. Apparent attenuation above 100% is possible with FG below 1.000 and is not clamped. No universal low-attenuation diagnosis or fermentation-failure threshold is applied.

Smart gravity input

Enter 1.060, 1,060, 1060 or 60 for the same SG 1.060. Direct SG is accepted from 0.900–1.300; integer-like compact readings 1000–1300 divide by 1000; integer-like shorthand points 0–300 become 1 + points/1000. An explicit points suffix also supports fractional points, such as 0.5 points = 1.0005. A trailing separator remains editable. Gravity fields deliberately interpret both dot and comma as decimal punctuation, even in en-US: 1,060 means SG 1.060, never a grouping separator. Grouped or mixed-punctuation gravity strings are rejected. Other decimal controls use the shared locale-friendly input parser.

Hydrometer temperature correction

Hydrometer correction is an approximation. Vinolab documents corrected SG = observed SG × P(sample °F) / P(calibration °F), where P(T) = 1.00130346 − 0.000134722124T + 0.00000204052596T² − 0.00000000232820948T³. Convert °C to °F with °F = °C × 9/5 + 32; inverse °C = (°F − 32) × 5/9. Supported sample ranges are 0–60°C for a 20°C/68°F calibration, or 0–55°C for a 15°C/59°F calibration. Choose the basis printed on the instrument; other calibrations and out-of-range temperatures reject. Corrected SG must also stay within 0.900–1.300. Correction in ABV mode uses separate OG/FG sample temperatures and the same calibration. It does not remove other instrument or sampling errors. Formula and range reviewed October 3, 2026.

Target ABV and target FG

To solve Target FG: FG = OG − target ABV / 131.25. OG 1.065 with target 7% gives 1.011666666… internally, displayed approximately 1.012. The unrounded internal value remains visible. To solve Target ABV instead, enter OG and target FG and reuse the forward equation. Targets are algebraic scenarios, not predictions that yeast will reach a gravity. A solved FG below 0.900 triggers a scenario warning without clamping. Target ABV input is 0–30%; target FG input uses the normal SG bounds.

Worked examples

1. OG and FG

OG 1.060, FG 1.012: gravity difference 0.048, drop 48 points. 0.048 × 131.25 ≈ 6.30% ABV; 0.048 / 0.060 × 100 = 80% apparent attenuation.

2. Gravity-point input

60 points → 1.060; 12 points → 1.012. The same readings produce estimated ABV 6.30%.

3. Target ABV

OG 1.065, target 7%: 1.065 − 7/131.25 ≈ 1.0116667. The three-decimal display is approximately 1.012; internal values are unrounded.

4. Invalid reading order

OG 1.045, FG 1.052: FG exceeds OG. Check whether readings were reversed or require correction; no normal negative ABV is shown.

Assumptions and limitations

The 131.25 equation is an educational estimate based on two readings. It does not measure laboratory alcohol content or fermentation completion. Brewing Check reports only structural issues: reversed readings, no drop, a drop below 2 points, and attenuation denominator context. These checks do not assess yeast health, infection, recipe quality or pressure safety. No bottling advice or fermentation-complete guarantee is provided. Expected readings are assumed already temperature-corrected; compare one current batch with one expected pair, using current minus expected differences. No history or saved brew data is included. Inputs remain in memory; there are no accounts, persistent storage, URL state or network calculations. Numeric fields are bounded to 32 characters; gravity to 0.900–1.300, target ABV to 0–30%, and correction temperatures to source-documented ranges.

FAQ

How do I calculate ABV from OG and FG?

Subtract FG from OG and multiply by 131.25 for the approximate percentage. The default 1.060 − 1.012 gives 6.30%.

What is original gravity?

OG is the specific-gravity reading before fermentation, comparing wort density with water.

What is final gravity?

FG is the later specific-gravity reading entered for the estimate. It reflects overall density, including the effects of alcohol and remaining extract.

What are gravity points?

They are thousandths above SG 1.000: 60 points means SG 1.060. The drop from 60 to 12 points is 48 points.

What does apparent attenuation mean?

It is the density-based percentage drop relative to OG above water, calculated as (OG − FG)/(OG − 1) × 100. It is not real attenuation or fermentation efficiency.

Can I enter 1060 instead of 1.060?

Yes. 1060, 60, 60 points, 1.060 and 1,060 all mean SG 1.060 here. Comma in gravity fields always means decimal punctuation.

Why might my hydrometer reading need temperature correction?

Density changes with temperature. Compare the sample temperature with the instrument’s calibration and use the bounded approximation when appropriate.

How do I calculate target FG for a target ABV?

Subtract target ABV divided by 131.25 from OG. OG 1.065 and target 7% produce approximately 1.012, without predicting actual fermentation.

Why is this ABV result only an estimate?

The gravity-to-alcohol relationship is simplified and readings have measurement uncertainty. Alternative formulas can differ, particularly at higher gravities.

What should I do if FG is higher than OG?

Check whether the readings were reversed or need correction. The calculator flags the order and does not present negative alcohol as a normal result.

Sources

Reviewed October 3, 2026. The sources explain the formula, correction bounds and measurement terminology; they do not endorse BuzCalculator. Our documented parser and validation rules define this implementation.

• Brewer’s Friend: standard ABV equation and approximation limits (opens in a new tab)
• Vinolab: hydrometer temperature polynomial and supported ranges (opens in a new tab)
• BeerSmith: apparent and real attenuation (opens in a new tab)
• American Homebrewers Association: accurate hydrometer readings (opens in a new tab)