IBU Calculator
International Bitterness Units (IBU) measure the concentration of isomerized alpha acids in beer, the compounds responsible for perceived bitterness. The Tinseth model calculates IBU from hop weight, alpha acid percentage, boil time, wort gravity and batch volume, with utilization rising steeply in the first 20 minutes and diminishing after that. Higher gravity wort reduces extraction.
Bitterness from one hop addition. Add up the additions in your recipe to get the total for the batch.
The Tinseth formula
This calculator and Brewgravity both use Tinseth’s utilisation model:
utilisation = 1.65 × 0.000125(G−1) × (1 − e−0.04t) / 4.15
IBU = weight(g) × alpha% × utilisation × 1000 / volume(L)
Most of the bitterness comes in the first 20 minutes; returns diminish fast after that. Higher gravity wort extracts less.
Form corrections
- Pellets — ~10% better extraction than whole leaf.
- First wort — treated as a longer boil addition with slightly better utilisation.
- Whirlpool at 85 °C — roughly a third of boil utilisation.
- Dry hops — no measurable IBU contribution.
Tinseth vs Rager
Rager predicts 20–30% higher IBU for the same addition. Both are fitted to different data. Pick one and stick with it — the absolute number matters less than consistency across your recipes. Brewgravity uses Tinseth throughout.
Reference
BJCP style pages list IBU ranges for each style. The hop alpha acid chart has typical alpha figures by variety.
IBU Calculator — questions
Why does my calculated IBU not match my measured IBU?
Lab-measured IBU and calculated IBU routinely differ by 20% or more. Calculations assume complete, uniform extraction; real kettles have hop crowns, uneven boils and losses to trub. Use the number for comparison between your own recipes rather than as an absolute.
How many IBU should my beer have?
It depends on the style and on the gravity. A helpful cross-check is the BU:GU ratio — IBU divided by gravity points. Around 0.5 is balanced, below 0.4 reads malty, above 0.8 reads bitter.
Do dry hops add bitterness?
Not in the IBU sense — there is no boil, so almost no isomerisation. Heavily dry-hopped beers can taste sharper from hop polyphenols, but that will not show up in an IBU measurement or calculation.
IBU that recalculates every time you change a hop
Add, remove or adjust a hop addition in Brewgravity and the total IBU updates instantly — Tinseth, same formula, no separate calculator tab.
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