IBU Calculator (Tinseth Hop Bitterness)
International Bitterness Units for up to four hop additions with the Tinseth formula — alpha acid, weight, boil time, batch size and boil gravity — plus the Rager estimate and bitterness ratio.
How it works
IBU = Σ [ weight (g) × alpha (%/100) × 1000 × utilisation ÷ litres ]; utilisation = 1.65 × 0.000125^(BG − 1) × (1 − e^(−0.04·t)) ÷ 4.15 (× 1.1 for pellets)
Bitterness comes from alpha acids isomerised during the boil, and Glenn Tinseth’s formula — the one most brewing software uses — estimates how much of each hop addition’s alpha acid ends up as iso-alpha acids in the beer. Utilisation rises with boil time (levelling off after about an hour) and falls in denser wort, captured by the “bigness” factor; pellets release about 10% more than whole cones. Real IBUs also depend on hop age, boil vigour, whirlpool time and dry hopping (which adds perceived bitterness without contributing much to the Tinseth number), so treat the result as a recipe design tool and a way to compare batches, not an analytical measurement. The bitterness-to-gravity ratio (BU:GU) is a quick read on balance.
Worked example
20 L at boil gravity 1.050: 30 g of 12% pellets for 60 min (≈ 46 IBU), 25 g of 6.5% for 15 min (≈ 10), 30 g of 6.5% at 5 min (≈ 5) — about 61 IBU, BU:GU 1.09 against an OG of 1.056: a bitter American IPA.
Frequently asked questions
Do whirlpool / flameout hops add IBUs?
Yes — isomerisation continues above ~80 °C. Many brewers enter a hop stand at 80–90 °C as roughly a 10–15 minute addition, or use software with a whirlpool utilisation model.
Why do Tinseth and Rager differ so much?
They were fitted to different breweries’ data; Rager predicts higher utilisation, especially for long boils. Pick one and stay consistent so your recipes compare to each other.
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This calculator is for educational purposes. Double-check important results before acting on them.