The IBU Tinseth Calculator estimates the bitterness of your beer in International Bitterness Units using Glenn Tinseth’s widely adopted utilization model. Enter each hop addition with its weight, alpha-acid percentage, and boil time, plus your wort gravity and batch volume, and the tool sums them into a total IBU figure.
How it works
Bitterness comes from alpha acids in hops, which only become bitter once they isomerize during the boil. Tinseth models that conversion as a single utilization factor:
utilization = bigness factor × boil-time factor
where
- bigness factor =
1.65 × 0.000125 ^ (gravity − 1)— utilization falls as boil gravity rises - boil-time factor =
(1 − e^(−0.04 × minutes)) ÷ 4.15— utilization rises with boil time, then plateaus
Each addition’s bitterness is then:
IBU = utilization × (AA% × weight_g × 1000) ÷ (volume_L × 10)
The × 1000 converts grams of alpha acids to milligrams, and dividing by
volume × 10 yields milligrams per litre — which is exactly one IBU.
Worked example
A 20 L batch boiled at 1.050 with 30 g of 12% AA hops at 60 minutes gives a
boil-time factor near 0.219 and a bigness factor near 0.986, for roughly
0.216 × (12% × 30 × 1000) ÷ (20 × 10) ≈ 39 IBU from that single addition. Late
additions at 15 and 5 minutes add aroma but far fewer IBU because the boil-time
factor is much smaller.
Tips and notes
Most modern IPAs land between 40 and 70 IBU, balanced bitters around 25–35, and lagers between 8 and 25. Tinseth tends to read a little lower than the older Rager method, so pick one formula and stick with it for consistency across batches. Adjust by taste over time — perceived bitterness also depends on malt sweetness and residual gravity.