IBU Calculator (Tinseth)
Enter each hop addition with weight, alpha acid and boil time, plus your boil gravity and batch size, to get total bitterness and the per-addition breakdown.
Results
| Addition | Utilization | IBU |
|---|---|---|
| Cascade 28 oz · 6% AA · 60 min | 0.231 | 152.8 |
How the Tinseth formula works
Each addition contributes IBU = AA% × ounces × utilization × 74.9 ÷ gallons. Utilization combines a gravity bigness factor (stronger wort extracts fewer iso-alpha acids) with a time factor that decays exponentially - a 60-minute boil extracts roughly 20-25%, a 5-minute charge under 5%. Tinseth is the most widely used homebrew model; perceived bitterness saturates around 100 IBU.
Bitterness is only half the recipe: size the alcohol backbone with the ABV calculator, and measure the boil gravity that drives utilization using the hydrometer temperature correction tool.
Frequently asked questions
Why does the same hop addition yield fewer IBUs in strong wort?
Iso-alpha acids isomerize and dissolve less readily in denser wort. Tinseth models this with a gravity "bigness" factor: the same ounce of hops in a 1.080 imperial stout gives roughly two-thirds the bitterness it would in a 1.040 session ale. That is why the calculator asks for boil gravity, not just hop amounts.
Do late additions contribute any bitterness?
Some, but not much. Utilization decays exponentially with boil time: a 60-minute addition extracts roughly 20-25% of its alpha acids, a 15-minute charge about 8%, and a 5-minute whirlpool-style addition under 5%. Late hops are mostly about aroma and flavor; if you need bitterness, put hops in at the start of the boil.
Why does my beer taste less bitter than the calculated IBU?
IBU measures dissolved iso-alpha acids, not perceived bitterness. Perception depends on the malt balance - the same 40 IBU reads much bitterer in a 1.040 pale ale than a 1.080 stout - plus water chemistry (sulfate sharpens bitterness), hop freshness, and age: IBUs fade noticeably within months. Use the number for recipe design and consistency, not as a taste prediction.
Do I count a whirlpool or hop-stand addition in the boil time?
Count only time at or near boiling. A 20-minute whirlpool at 80 C (175 F) isomerizes a little alpha acid, but far less than the exponential model assumes for 20 boiling minutes - enter whirlpool additions as 0-5 minutes if you want a rough allowance, or leave them out and treat them as aroma-only.