Calculating Homebrew IBU with the Tinseth Formula
IBU (International Bitterness Units) measures the concentration of isomerized alpha acids dissolved in a beer, and it's the number homebrewers rely on most to predict how bitter a recipe will taste. This calculator uses the Tinseth formula, the industry standard among homebrewing software.
Tinseth's formula multiplies two factors to get utilization. The first is a gravity-based loss factor: higher wort gravity makes alpha acids harder to dissolve, lowering utilization. The second is a time-based factor that rises with boil time but flattens out as the boil goes on. Multiplying utilization by the hop's alpha acid content and weight, then dividing by batch volume, gives the final IBU.
Hops added without boiling, like dry hops, aren't captured by this formula — they contribute aroma and flavor but essentially no measurable IBU. To raise bitterness, increase the amount of hops added early in the boil or pick a higher alpha acid variety. To preserve aroma, add hops late in the boil or right after flameout instead.
Frequently Asked Questions
IBU (International Bitterness Units) measures the concentration of isomerized alpha acids in beer. Higher numbers mean more bitterness, with typical lagers around 5-20 and IPAs often 40-70 or higher.
A longer boil increases alpha acid utilization and therefore IBU, but the gains taper off past 60 minutes. Shorter boils preserve hop aroma, while longer boils favor bitterness.
Higher wort gravity reduces how efficiently alpha acids dissolve and isomerize, so the same hop addition yields a lower calculated IBU in a denser wort.