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Redmoon Converters
🍺 Home Brewing

IBU Hop Bitterness Calculator (Tinseth & Rager)

Calculate beer IBUs with Tinseth or Rager utilisation. Multiple hop additions, whirlpool / hop-stand, pellet / leaf / cryo, and BU:GU ratio output.

Built and maintained by Paul Clark, Redmoon Software · Checked against what this tool computes on

Used for BU:GU only.
Estimated OG or wort gravity during boil.
WeightUnitAA%Boil (min)Form
Total IBU (Tinseth)
0.0
BU:GU ratio —
AdditionUtilizationIBU
Quick reference

Tinseth formula:

Tinseth: bigness = 1.65 × 0.000125^(boil_gravity − 1)

timeFactor = (1 − exp(−0.04 × boil_time)) / 4.15

utilization = bigness × timeFactor × form_modifier

Rager: utilization% = 18.11 + 13.86 × tanh((minutes − 31.32) / 18.27), divided by (1 + gravity adjustment), where the adjustment is (boil_gravity − 1.050) / 0.2 above 1.050 and zero below it. Rager typically reads 30–40% higher than Tinseth for the same addition — pick the one your recipes are calibrated against.

Cryo/lupulin pellets carry no extra utilisation multiplier here: their concentration is already captured by the roughly doubled alpha-acid percentage printed on the package, so enter that AA% and the maths follows. A whirlpool/hop-stand addition is modelled as 15 minutes of equivalent contact time regardless of the boil time entered.

IBU = AA% × weight_g × utilization × 1000 / batch_L

Form modifiers: pellet 1.0, leaf 0.92, cryo 2.0. Whirlpool additions are modeled as a 15-minute boil equivalent. Dry hops contribute 0 IBU. BU:GU ratio = IBU / gravity-points (e.g. 1.050 → 50).

How it works

Every addition is scored with Tinseth utilisation. A bigness factor of 1.65 × 0.000125^(boil gravity − 1) penalises higher-gravity worts, a time factor of (1 − e^(−0.04 × minutes)) / 4.15 rewards longer boils, and the two multiply together with a form modifier to give utilisation. Bitterness is then alpha acid percentage times weight in grams times utilisation times 1000, divided by batch volume in litres. Each row shows its own utilisation figure so you can see where the bitterness is coming from.

Boil gravity, alpha acid percentage and boil time move the result hardest. At the default 1.050, a 60-minute pellet addition reaches about 23% utilisation, while the same hop at 15 minutes manages only 11%. Form matters too: pellets score 1.0, leaf hops 0.92, cryo 2.0, whirlpool additions are modelled as a fixed 15-minute boil equivalent regardless of the minutes you type, and dry hops contribute nothing. The BU:GU output divides total IBU by gravity points, so 1.050 counts as 50.

Tinseth is a model fitted to traditional boil-hopped beer and it drifts on modern recipes built around large late and whirlpool charges. The whirlpool option in particular is a single flat assumption — it takes no account of how hot your stand is or how long it runs — and the cryo modifier simply doubles utilisation, which will over-count if you have also entered the higher alpha acid figure printed on a cryo package. First-wort and mash hopping are not modelled, and measured IBUs from a lab rarely match any calculator exactly.

Frequently asked questions

Do dry hops add IBUs?

Not in this calculator. Selecting Dry hop sets both the form modifier and the effective time to zero, so the addition contributes 0 IBU. Dry hopping adds aroma and a perception of bitterness, but very little measurable iso-alpha acid, since there is no heat to isomerise.

How are whirlpool and hop stand additions calculated?

As a 15-minute boil equivalent with a form modifier of 1.0. Whatever you type into the Boil (min) column is ignored for whirlpool rows — the tool substitutes 15 minutes. That gives roughly 11% utilisation at 1.050 boil gravity.

Why does higher gravity wort give fewer IBUs?

The bigness factor, 1.65 × 0.000125 raised to the power of the gravity above 1.000, shrinks as wort gets denser. Sugar-rich wort extracts and isomerises alpha acids less efficiently, so a big stout needs more hops than a session beer for the same bitterness.

Do pellets give more bitterness than whole leaf hops?

Slightly. Pellets carry a form modifier of 1.0 and leaf hops 0.92, so identical weights of leaf give about 8% fewer IBUs. Cryo is treated as 2.0 — double utilisation — reflecting its concentrated lupulin content.

What does the BU:GU ratio tell me?

It is total IBU divided by gravity points, where 1.050 counts as 50. It describes bitterness relative to malt sweetness rather than in isolation, so the number stays comparable when you scale a recipe up in strength. The default two-hop bill lands around 1.24.

Tinseth and Rager do not agree, and neither is wrong

Both formulas model the isomerisation of alpha acids during the boil, and they were fitted differently — Rager generally returns higher numbers than Tinseth for the same recipe, and the gap widens with boil time and gravity. Neither is more correct; they are different models of a process that resists precise modelling.

What matters is consistency. Pick one and use it for every recipe, because comparing a Tinseth figure against a Rager one tells you about the formulas rather than about the beers.

Why calculated IBU is not measured IBU

Real utilisation varies with boil vigour, hop form (pellets extract better than whole cones), wort gravity, kettle geometry and how quickly the wort is chilled afterwards. Two brewers following one recipe on different systems can land 15% apart and both be brewing correctly.

Alpha acid content also drifts: the figure on the packet is measured at harvest and declines in storage, so year-old hops deliver less bitterness than their label claims.

Perceived bitterness is a further step removed, because it is balanced against residual sweetness. A 40 IBU beer at high final gravity tastes far less bitter than a 40 IBU beer that finished dry, which is why bitterness-to-gravity ratio is often more useful than IBU alone.

Where these numbers come from

The standard or formula behind this tool, so you can check it rather than take it on trust.

  • Tinseth, G. — Hop utilisation model.

    Models isomerisation from alpha acid, boil time and wort gravity. Real utilisation varies with boil vigour, hop form and kettle geometry, so two brewers following one recipe can land 15% apart and both be right.

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