IBU Calculator
Hop bitterness in IBU using the Tinseth and Rager models, for any number of hop additions.
Hop additions
How it works
Each hop addition contributes bitterness equal to its alpha-acid concentration times a utilization factor. Tinseth derives utilization from boil gravity and time; Rager uses a time-based curve with a gravity adjustment above 1.050.
Tinseth: U = 1.65 × 0.000125^(SG−1) × (1 − e^(−0.04t)) / 4.15
IBU = Σ U × (AA% × grams × 1000 / litres)
Sources: Glenn Tinseth's hop utilization page; Rager (Zymurgy, 1990) as reproduced at BrewWiki.
IBU models are estimates - real bitterness varies with hop freshness, whirlpool/late additions and utilisation. Pick one model and stay consistent so your recipes are comparable; Tinseth is the common default.
Frequently asked questions
- What is the Tinseth IBU formula?
- Tinseth estimates hop utilization from boil gravity and boil time, then multiplies by the concentration of alpha acids added. Utilization rises with boil time and falls as wort gravity rises. It is the most widely used model in homebrewing software.
- Tinseth vs Rager - why do they differ?
- Rager generally predicts higher IBUs than Tinseth for the same hops, especially at longer boil times, and it applies a gravity adjustment above 1.050. Neither is "correct" - pick one and stay consistent so your recipes are comparable. This tool shows both.
- Should I use pellet or whole-hop utilization?
- Pellets are usually credited with about 10% higher utilization than whole/leaf hops. Toggle the form factor to apply roughly +10% for pellets.