IBU Calculator
Bitterness for a whole hop schedule by the Tinseth model, with the two factors behind the number shown rather than hidden inside the result.
Average gravity during the boil, not final OG. Higher gravity lowers utilization.
Hop schedule
| Weight (oz) | Alpha acid % | Boil (min) | IBU | |
|---|---|---|---|---|
| 17.3 | ||||
| 8.6 |
The two factors behind utilization
bigness = 1.65 × 0.000125^(1.050 − 1) = 1.0528
boil time (60 min) = (1 − e^(−0.04 × 60)) ÷ 4.15 = 0.2191
utilization = 0.2307 = 23.1%
How the Tinseth model works
Hops do not make beer bitter by sitting in it. The alpha acids have to isomerise, a heat-driven reaction that is slow, incomplete, and hindered by dissolved sugar. Tinseth models the fraction that actually converts — the utilisation — as the product of two factors, then multiplies it by how much alpha acid you added per unit volume.
The bigness factor handles gravity: 1.65 × 0.000125^(gravity − 1). The boil time factor handles contact time: (1 − e^(−0.04 × minutes)) ÷ 4.15. Multiply them for utilisation, and the rest is bookkeeping — weight, alpha acid percentage, and batch volume.
Worked example
One ounce of 5% alpha acid hops, boiled 60 minutes, in 5 gallons at 1.050 boil gravity.
Utilisation works out at 23.1%, and the full equation gives 17.3 IBU.
Move those same hops to a 15 minute addition and the contribution falls to 8.6 IBU — the same hops, roughly half the bitterness.
What utilisation looks like across the range
Both effects in one table: time along the top, gravity down the side, utilisation as a percentage in each cell.
| Boil gravity | 10 min | 20 min | 30 min | 45 min | 60 min | 90 min |
|---|---|---|---|---|---|---|
| 1.040 | 9.1% | 15.3% | 19.4% | 23.2% | 25.2% | 27.0% |
| 1.050 | 8.4% | 14.0% | 17.7% | 21.2% | 23.1% | 24.7% |
| 1.060 | 7.6% | 12.8% | 16.2% | 19.4% | 21.1% | 22.6% |
| 1.070 | 7.0% | 11.7% | 14.8% | 17.7% | 19.3% | 20.6% |
| 1.080 | 6.4% | 10.7% | 13.5% | 16.2% | 17.6% | 18.8% |
| 1.090 | 5.8% | 9.8% | 12.4% | 14.8% | 16.1% | 17.2% |
Common mistake
Entering original gravity instead of boil gravity on a partial-boil batch. If you boil 3 gallons of concentrated wort and top up to 5, the wort the hops actually sit in is far denser than the finished beer. Using the diluted OG will overstate your utilisation and leave the real beer less bitter than the recipe promised.
Keep going
- Bitterness is usually judged against strength -- the bitterness-to-gravity ratio -- so the ABV calculator supplies the other half of that balance. ABV Calculator
Frequently Asked Questions
Why does late-addition hopping add so little bitterness?
Bitterness comes from isomerising alpha acids, and that reaction needs sustained heat. The boil time factor is (1 − e^(−0.04 × minutes)) ÷ 4.15, which rises steeply early and then flattens — so a 60 minute addition contributes many times what the same hops give at 10 minutes, and a flameout addition contributes essentially nothing on this model despite adding plenty of aroma.
Why does a stronger beer get less bitter from the same hops?
Alpha acids isomerise less efficiently in sugar-rich wort. Tinseth captures that with the bigness factor, 1.65 × 0.000125^(gravity − 1), which falls as gravity rises. Brew the identical hop schedule at 1.080 instead of 1.040 and you lose roughly 30% of the bitterness.
Should I use boil gravity or original gravity?
Boil gravity — the average gravity of the wort while the hops are actually in it. On a full-volume boil the two are close. On a partial boil topped up with water afterwards, boil gravity is much higher than final OG, and using OG instead will overstate your bitterness significantly.
Why do different calculators give different IBUs for the same recipe?
Because they use different models. Tinseth, Rager and Garetz each fit the utilisation curve differently, and Rager in particular tends to read higher. None is definitively correct — they are empirical fits to a messy reaction. What matters is picking one and staying with it so your recipes stay comparable to each other.
Does this handle whirlpool, dry hop or first wort hopping?
Not as distinct modes. Dry hopping adds aroma but essentially no measurable IBU, so it is correctly excluded. Whirlpool and first wort additions do contribute bitterness that a plain boil-time model handles only approximately — enter an equivalent boil time if you want an estimate, and treat the result as rough.
Is measured IBU the same as calculated IBU?
No. Laboratory IBU measures absorbance of bitter compounds in the finished beer, while these models predict isomerisation from the recipe. Real losses to trub, yeast and packaging mean measured values often come in below calculated ones, particularly in heavily hopped beers.
Source and an honest caveat. Glenn Tinseth's original publication at realbeer.com has been retired — the domain now redirects to a site-closure notice — so the formula components used here were taken from Solid Beer's write-up of the Tinseth and Rager formulas, retrieved 19 September 2026, and cross-checked against other published implementations. Rager's model is deliberately not offered here: its gravity adjustment is published but its utilisation lookup table is not, and implementing it from a guessed table would be worse than leaving it out.
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