United KingdomTier 1
IBU calculator (Tinseth)
Batch volume and boil gravity, plus up to three hop additions. Total IBU out, with each addition's contribution.
Free·No sign-up·Last checked 2026-08-27
Formula — Tinseth (metric)
Bigness factor = 1.65 × 0.000125^(OG − 1)
Boil time factor = (1 − e^(−0.04 × time)) ÷ 4.15
Utilization = bigness factor × boil time factor
IBU (per addition) = utilization × (AA decimal × weight_g × 1000) ÷ batch_L
Worked example. 28 g at 11% AA for 60 min in a 19 L batch at 1.050 OG contributes about 37.4 IBU.
Method
Metric-native Tinseth formula
This uses grams and litres directly rather than the imperial constant (7490) some American calculators use for ounces and gallons — the underlying isomerization model is identical, just expressed in the units this page asks for.
Questions
Alpha acids isomerize less efficiently in a denser wort, so the same hop addition contributes fewer IBU in a high-gravity boil than in a thinner one — the Tinseth "bigness factor" models that drop directly.
Utilization rises quickly at first, then levels off — the time factor is asymptotic. A hop needs roughly 60–90 minutes to approach its full isomerization potential.
No — Tinseth models boil-kettle isomerization only. Whirlpool and dry hop additions contribute flavour and aroma but negligible measured bitterness, and different models exist for estimating whirlpool IBU.