IBU Calculator
Each hop's bitterness, summed by the Tinseth model. More alpha acid and boil time raise it; higher gravity lowers it.
IBU stands for International Bitterness Units — how brewers measure hop bitterness. A light lager sits near 10 IBU; a West Coast IPA pushes 60+. The calculator above sums every hop addition: boil, whirlpool, first wort, mash, and dry hop all contribute, and each is modeled differently.
How We Calculate It
Boil additions use the Tinseth model, the industry standard. It accounts for two things: how wort gravity suppresses extraction, and how boil time increases it with diminishing returns.
W = hop weight (oz), α = alpha acid %, U = utilization factor, V = batch volume (gal).
Beyond the Boil
Modern recipes use hops in more places than the boil, and the calculator handles each:
- Whirlpool & hop stand — isomerization slows but continues below boiling. Utilization is scaled by temperature (about 29% of the boil rate at 80°C, dropping to zero below ~60°C).
- Dry hops — humulinones formed during pellet processing dissolve without heat and add measurable bitterness. A heavy dry hop adds roughly 12 IBU.
- First wort hops — added during lautering, they get the full boil plus extra contact; we treat them as the boil time plus 20 minutes.
- Mash hops — most alpha acids wash out with the grain, so we apply a standard 20% utilization.
Worked Example
One ounce of Cascade (7% alpha acid) boiled 60 minutes in 5 gallons of 1.050 wort:
Gravity factor = 1.65 × 0.0001250.050 = 1.053
Time factor = (1 − e−2.4) / 4.15 = 0.219
Utilization = 1.053 × 0.219 = 23.1%
IBU = (1 × 7 × 0.231 × 75) / 5 = 24.2 IBU
Where This Comes From
The Tinseth model has been the industry standard since 1995, and our dry-hop model follows research on humulinones dissolving without heat. For the full derivation — including whirlpool temperature scaling and the dry-hop humulinone model — see Understanding IBU & Bitterness.
What is the Tinseth formula?
Tinseth (1995) estimates hop utilization from wort gravity (higher gravity lowers extraction) and boil time (longer boils extract more, with diminishing returns past about 60 minutes). IBU = weight × alpha-acid% × utilization × 75 ÷ volume.
Do whirlpool and hop-stand additions add IBU?
Yes. Isomerization slows but doesn't stop below boiling. We scale the Tinseth utilization by a temperature factor — roughly 29% of the boil rate at 80°C, dropping to zero below about 60°C.
Do dry hops add bitterness?
A little. Humulinones formed during pellet processing dissolve without heat and add measurable bitterness — a heavy dry hop (about 8 g/L at 12% AA) adds roughly 12 IBU. We model the humulinone contribution plus a small amount of non-isomerized alpha acid.
What IBU should my beer be?
It depends on style: a light lager sits near 8–12 IBU, an American pale ale 30–45, a West Coast IPA 50–70+. Perceived bitterness is also balanced by malt sweetness, so the same IBU tastes different at different gravities.
Why don't my IBUs match another calculator?
Calculators use different utilization models (Tinseth vs Rager vs Garetz) and different assumptions for whirlpool and dry-hop bitterness. We use Tinseth for the boil and add explicit whirlpool, first-wort, mash, and dry-hop handling, so totals can differ by several IBU.