Wine ABV Calculator

A refractometer measures how much light bends when passing through a liquid. Before fermentation this works perfectly for measuring sugar concentration. After fermentation, alcohol in the wash bends light differently to water — making the reading appear lower than the actual gravity. If you use the raw refractometer reading as your FG you will overestimate your ABV.

This calculator applies the Terrill correction formula, which uses both the original Brix reading and the post-fermentation apparent Brix to recover the true final gravity:

Where Ri = initial Brix (OG reading) and Rf = apparent final Brix (post-fermentation refractometer reading). This is the most widely accepted correction formula for homebrewing and home distilling.

Most hydrometers are calibrated at 20°C (68°F). If your sample is warmer, the liquid is less dense and the hydrometer floats higher, giving a reading that is lower than the true gravity. The correction runs about +0.001 SG per 5°C just above calibration temperature and grows with the gap, reaching roughly +0.006 SG at 40°C. This calculator applies the polynomial correction formula for accurate results across a wide temperature range.

Grape must contains almost no unfermentable dextrin. Wine yeast can consume nearly all of the available sugar, so a dry wine ferments far closer to completion than a beer does.

Once the sugar is gone, what remains is mostly water and ethanol. Ethanol is less dense than water (a specific gravity of about 0.789), so a dry wine routinely finishes below 1.000, commonly between 0.990 and 0.996. A hydrometer reading under 1.000 is normal here, not a fault.

Typical range: original gravity 1.080 to 1.100, final gravity 0.990 to 0.996. Because apparent attenuation is calculated against a final gravity below 1.000, wine can show an apparent attenuation above 100%, which is a quirk of the arithmetic rather than an impossible fermentation.

One caution on accuracy: the simple (OG − FG) × 131.25 approximation is calibrated around beer-strength worts. It drifts at the higher starting gravities common in wine, where the Balling-derived calculation is the more reliable choice.

Apparent attenuation tells you what percentage of the available sugars have been fermented. For most dry table wines this should approach 98–100%. A reading well below that with gravity stable for several days points to a stuck fermentation.

A dry wine typically shows apparent attenuation between 90 and 100%, and can read above 100% when the final gravity falls below 1.000. A stuck wine fermentation more often reflects high alcohol stressing the yeast or a nitrogen shortfall than a temperature problem.