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 is approximately +0.001 SG per 5°C above calibration temperature. This calculator applies the polynomial correction formula for accurate results across a wide temperature range.

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.

Most dry table wines ferment to 98–100% apparent attenuation, since wine yeasts are typically selected for high alcohol tolerance and complete sugar conversion. A must that stalls well short of that, especially above 1.010 SG, is worth checking for temperature, nutrient deficiency or a yeast struggling with high starting sugar or alcohol.