What formula does the wine ABV calculator use?

The calculator uses two formulas side by side. The standard simplified formula is ABV (%) = (OG − FG) × 131.25. This is accurate within about 0.2% for typical wine gravities. The Miller formula — ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794) — is more precise for high-gravity wines and meads above OG 1.100, where the standard formula can underestimate by 0.3–0.5%.

What is specific gravity and how do I measure it?

Specific gravity (SG) compares the density of a liquid to pure water (SG 1.000). Sugar dissolved in water raises the density above 1.000, so grape juice and honey-must start around 1.070–1.130 before fermentation. As yeast converts sugar to alcohol (which is lighter than water), the gravity falls. A hydrometer floating in a graduated tube reads the SG directly. Most readings are given to three decimal places, e.g. 1.085.

Can I use a refractometer instead of a hydrometer for final gravity?

A refractometer is ideal for measuring OG before fermentation, but it gives inaccurate FG readings once alcohol is present because alcohol bends light differently from sugar. The Brix mode in this calculator converts your refractometer reading using the standard approximation — treat the FG result as an estimate only. For a precise final reading, use a hydrometer and temperature-correct if needed.

What is apparent attenuation?

Apparent attenuation is the percentage of fermentable sugars the yeast has consumed, calculated as (OG points − FG points) / OG points × 100. A dry wine with OG 1.090 finishing at FG 0.993 has an apparent attenuation of about 97%, meaning nearly all the original sugar has been fermented. Lower attenuation indicates residual sweetness or a stuck fermentation.

How accurate is the residual sugar estimate?

The residual sugar figure is a rough estimate derived from the final gravity using the relationship RS ≈ (FG − 0.9964) × 2617. It is useful for understanding sweetness category (dry, off-dry, sweet) but not precise enough for labelling under EU or US wine regulations, which require laboratory analysis. Dry wines below FG 0.998 will show near-zero residual sugar; wines finishing above 1.010 will show noticeable sweetness.

What OG should I target for a specific wine ABV?

A useful rule of thumb is that every 7–8 gravity points (0.007–0.008 SG) above 1.000 yields roughly 1% ABV when fermented dry. To target 12% ABV, aim for an OG of about 1.084–1.092. For a 14% wine, target OG 1.098–1.106. Use this calculator in reverse: enter your target ABV and a typical dry FG (around 0.993) to work out what OG you need, then adjust your must with sugar additions (chaptalization) or water dilution.

Wine ABV Calculator — Gera Tools

A wine ABV calculator that converts your original gravity (OG) and final gravity (FG) into a precise alcohol by volume (ABV) percentage — the same calculation professional winemakers and brewers use every day. It also shows apparent attenuation, estimated residual sugar, and a sweetness classification, so you understand not just the strength of your wine but its character.

How it works

When grape juice, fruit must, or a honey-water solution ferments, yeast consumes dissolved sugars and produces ethanol and carbon dioxide. Because sugar is denser than water, the liquid’s specific gravity falls as fermentation progresses. The difference between the starting gravity (OG) and the ending gravity (FG) is directly proportional to the alcohol produced.

The standard ABV formula used by most home winemakers is:

ABV (%) = (OG − FG) × 131.25

The constant 131.25 comes from combining ethanol’s density (about 0.789 g/mL) with the relationship between gravity points and dissolved sugar concentration. This formula is accurate to within 0.2% for wines in the typical range of OG 1.070–1.120.

For high-gravity wines and meads (OG above 1.100), the calculator also shows the Miller formula, which corrects for the non-linear effect of high alcohol concentrations on density:

ABV (%) = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)

The difference between the two formulas is small for normal table wines but can reach 0.3–0.5% for a 16% port-style wine, where precision matters for labelling.

Worked example

A dry red wine starts at OG 1.090 (a Cabernet-style must) and ferments down to FG 0.995:

Gravity drop: 1.090 − 0.995 = 0.095 (95 gravity points)
Standard ABV: 0.095 × 131.25 = 12.47%
Miller ABV: 12.51%
Apparent attenuation: (90 − −5) ÷ 90 × 100 = ~94% (nearly fully dry)
Residual sugar: ≈ 1.5 g/L (bone dry)

A semisweet Riesling at OG 1.100 fermenting to FG 1.020:

Gravity drop: 0.080 (80 points)
Standard ABV: 0.080 × 131.25 = 10.5%
Residual sugar: ≈ 62 g/L (medium-sweet, noticeable sweetness on the palate)

Style	OG	FG	ABV (std)	Sweetness
Bone-dry white	1.075	0.993	10.7%	Dry
Classic dry red	1.090	0.995	12.5%	Bone dry
Off-dry Riesling	1.095	1.010	11.1%	Off-dry
Port-style	1.130	1.030	13.1%	Sweet
Dry mead	1.110	0.998	14.7%	Dry

Temperature and refractometer notes

Hydrometers are calibrated at a specific temperature — usually 15 °C (59 °F) or 20 °C (68 °F) depending on the instrument. If your must or wine is warmer than calibration temperature, the reading will be slightly low; cooler, slightly high. A correction of roughly +0.001 SG per 5 °C above calibration is a good rule of thumb.

Refractometers measure the bending of light (refractive index) through the liquid. Before fermentation, Brix readings convert cleanly to specific gravity. After fermentation starts, dissolved alcohol distorts the reading, so refractometer Brix values for FG are estimates only — use a hydrometer for a precise final gravity.

All calculations run entirely in your browser. No readings are uploaded or stored.