Hop Utilization Calculator

The Tinseth formula's gravity factor, f(gravity) = 1.65 × 0.000125^(wort gravity − 1), gets smaller as wort gravity rises, modeling the real chemistry that denser, sugar-heavier wort suppresses the isomerization reaction that converts alpha acid into bitterness. This calculator uses a single fixed gravity value for the whole boil, so entering the gravity at the time of the hop addition — not your final original gravity — gives the most accurate utilization estimate for that addition.

It doesn't, but the gain from 60 to 90 minutes is much smaller than the gain from 0 to 60, because the time factor f(time) = (1 − e^(−0.04 × boil time)) / 4.15 follows a diminishing-returns curve — most of the achievable utilization happens in the first 30-40 minutes, and additional boil time keeps adding IBU but at a steadily shrinking rate.

IBU accounts for how much of the hop's alpha acid actually isomerizes into bitterness given your specific boil time and wort gravity, via the full Tinseth formula. AAU is just hop weight times alpha acid percentage, with no time or gravity adjustment at all — it's a quick, simplified figure some recipes use for hop-bag sizing or scaling a recipe, not a bitterness prediction.

The chart sweeps boil time from 0 to 90 minutes while holding your entered wort gravity fixed at a single value, so it correctly shows sharply lower IBU for short boil times — that part matches real late-addition behavior. What it doesn't capture is that in an actual boil, gravity itself keeps rising as water evaporates, which would suppress utilization further as the boil progresses; this calculator's single-gravity-point model doesn't account for that rising concentration.