Calculator
IBU calculator
How bitter will my beer be?
IBU measures the concentration of isomerised alpha acids in the finished beer, in parts per million. It is a chemical measurement rather than a measure of perceived bitterness, and the two come apart in ways that matter: malt sweetness masks bitterness, so a 60 IBU barley wine can taste less bitter than a 35 IBU dry pilsner.
The calculated figure is also an estimate rather than an analysis. Utilisation — the share of alpha acid that actually isomerises — depends on boil vigour, wort gravity, hop form and time, and the standard formulas are empirical fits to that behaviour rather than physical laws. Treat the number as a design target and a way to compare one recipe with another, not as a value a laboratory would confirm.
Result
- IBU62 IBU
Working
IBU = Σ (utilisation × grams × alpha% × 10) ÷ litres, where utilisation = bigness × time factor
| Step | Expression | Value |
|---|---|---|
| Bigness factor | 1.65 × 0.000125^(SG − 1) | 1.0528 |
| Addition 1 — 30 g at 12% for 60 min | utilisation × g × AA% × 10 ÷ litres | 41.5 IBU (utilisation 23.1%) |
| Addition 2 — 40 g at 12% for 10 min | utilisation × g × AA% × 10 ÷ litres | 20.1 IBU (utilisation 8.4%) |
What it means
Treat the result as a target to brew consistently against rather than a prediction of what a lab would measure.
Worked example
The example above starts from these values. It is rendered on the server, so the formula, assumptions and limitations are all present whether or not you change anything.
- Result62 IBU
Inputs
| Batch volume | 20 L |
|---|---|
| Boil gravity | 1.050 |
| Hop additions | 2 |
How it is calculated
IBU = Σ (utilisation × grams × alpha% × 10) ÷ litres, where utilisation = bigness × time factor
What each term means
| bigness | Reduction in utilisation as wort gravity rises: 1.65 × 0.000125^(SG − 1) |
|---|---|
| time factor | (1 − e^(−0.04 × minutes)) ÷ 4.15 |
| alpha% | Alpha acid content of the hop, as a percentage |
Step by step
| Step | Expression | Value |
|---|---|---|
| Bigness factor | 1.65 × 0.000125^(SG − 1) | 1.0528 |
| Addition 1 — 30 g at 12% for 60 min | utilisation × g × AA% × 10 ÷ litres | 41.5 IBU (utilisation 23.1%) |
| Addition 2 — 40 g at 12% for 10 min | utilisation × g × AA% × 10 ÷ litres | 20.1 IBU (utilisation 8.4%) |
What this assumes
- Uses the Tinseth utilisation model, which is the most widely adopted of several competing models.
- Pellet hops; whole cones extract slightly less.
- Additions after flameout contribute no isomerised bitterness in this model.
Where it stops being reliable
- IBU models disagree with each other by 20% or more on the same recipe. Tinseth, Rager and Garetz all give different answers, and none is authoritative.
- Calculated IBU frequently differs substantially from measured IBU in the finished beer, because losses to trub, yeast and packaging are not modelled.
- IBU is not perceived bitterness. Residual sweetness, body and roast all change how bitter a beer tastes at the same measured value — a 60 IBU imperial stout tastes far less bitter than a 60 IBU West Coast IPA.
- Whirlpool and dry-hop additions contribute aroma and flavour that this number does not capture at all.
What the number means
Treat the result as a target to brew consistently against rather than a prediction of what a lab would measure.
Empirical approximation. A curve fitted to measured data. It has real error bars, and it is frequently quoted as though it were exact.
Sources: Tinseth hop utilisation model.