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:
- Bigness factor:
1.65 × 0.000125 ^ (1.050 − 1) ≈ 0.986 - Boil-time factor:
(1 − e^(−0.04 × 60)) ÷ 4.15 ≈ 0.219 - Utilization:
0.986 × 0.219 ≈ 0.216 - IBU:
0.216 × (0.12 × 30 × 1000) ÷ (20 × 10) ≈ 39 IBU
That is the bittering charge. Adding 10 g of the same hop at 15 minutes (for example) would produce only around 12 additional IBU due to the much smaller boil-time factor at shorter contact times. Dry hop additions and whirlpool/hop-stand additions at sub-isomerization temperatures are not modeled by Tinseth and contribute negligible calculated IBU.
Multiple additions and recipe planning
Most homebrew recipes use at least two hop additions:
- Bittering addition (60 min) — maximises IBU per gram of hops. Long boil time drives the boil-time factor close to its plateau.
- Flavour addition (10–20 min) — adds some bitterness plus hop-derived flavour compounds that survive the shorter boil.
- Aroma addition (0–5 min or flame-out) — contributes aroma oils. Very few IBU by Tinseth’s formula because the boil-time factor is tiny.
Add each addition as a separate row in this tool. The total IBU shown is the sum of all rows.
Tinseth versus other IBU formulas
The main alternatives are the Rager and Garetz formulas. Tinseth generally gives lower IBU figures than Rager for high-gravity worts and shorter boil times. Garetz additionally adjusts for dry-hopping, yeast type and fermentation conditions. Most homebrewing software defaults to Tinseth because it was developed from extensive measured data. Whichever you choose, consistency matters more than absolute accuracy: use the same formula across all your recipes so your IBU scale is internally comparable.
Reading the result in context
| Style | Typical Tinseth IBU |
|---|---|
| Lager / Pilsner | 8–25 |
| Wheat beer | 10–20 |
| Pale Ale | 25–45 |
| Balanced Bitter | 25–40 |
| IPA | 40–70 |
| Double IPA | 60–100 |
| Stout | 25–50 |
Perceived bitterness also depends on residual sweetness (final gravity) and water chemistry (sulphate-to-chloride ratio). A 40 IBU beer can taste sharp or round depending on those factors, so treat the IBU figure as a design parameter rather than a sensory guarantee.