Priming Sugar Calculator

This calculator figures out how much priming sugar to add at bottling time to reach a target carbonation level, expressed in volumes of dissolved CO2. The starting point is residual CO2 — the carbonation already locked into the beer from fermentation, which the calculator estimates from a temperature-based polynomial (converted from your entered Fahrenheit reading to Celsius first): warmer beer holds less dissolved CO2, so a beer that peaked at a warm fermentation temperature needs more added sugar than one that was cold-crashed, even for the same style target. Subtracting residual CO2 from your target CO2 volumes yields the amount you still need to add, which is then multiplied by batch volume and a fixed conversion factor of about 4 grams of corn sugar per gallon per volume of CO2 — a widely used homebrewing constant.

If you're using a sugar other than corn sugar (dextrose), the calculator applies a fermentability factor — table sugar at 0.91, honey at 0.77, dried malt extract at 0.73 — dividing the corn-sugar-equivalent amount by that factor, since a less-fermentable sugar source requires proportionally more mass to produce the same CO2. The result is reported in both grams and ounces. Because the residual-CO2 estimate is an approximation and doesn't account for time spent at various temperatures throughout fermentation and conditioning (only the single highest temperature you enter), treat the final number as a strong starting estimate — and always err toward slightly less sugar with bottle-conditioned Belgian-strength beers, where over-carbonation risks gushers or bottle bombs.