IBU Calculator: Hop Bitterness for Any Batch
Bitterness from every hop addition with the Tinseth formula, with Rager beside it, the BU:GU balance, and how much hop you need for a target IBU.
Loading the calculator…
How to use it
- Enter your wort. The volume in the kettle at the end of the boil, and the original gravity. Stronger wort pulls less bitterness from the same hops.
- Add each hop. Its alpha acid from the packet, the weight, and when it goes in: boil, first wort, whirlpool or dry hop. For a whirlpool or hop stand, enter the minutes and the temperature.
- Or work backwards. Switch to “Hops for a target IBU” to find how much bittering hop gets you to, say, 40 IBU.
The IBU formula
The calculator uses Glenn Tinseth’s formula, the one most recipes and Brewfather use:
IBU = utilization × alpha acid % × ounces × 74.9 ÷ gallons
Utilization = 1.65 × 0.000125^(OG − 1) × (1 − e^(−0.04 × minutes)) ÷ 4.15
In metric, use grams × 10 ÷ litres instead of ounces × 74.9 ÷ gallons. Example: 0.75 oz of a 12% hop boiled 60 minutes in 5.5 gallons of 1.050 wort has a utilization of 23.1%, so 0.231 × 12 × 0.75 × 74.9 ÷ 5.5 = 28 IBU.
Jackie Rager’s older formula is shown beside it. It reads higher, especially for long boils, and only adjusts for gravity above 1.050. Use the same formula the recipe was written with.
Hop utilization chart
| Boil time | 1.030 | 1.040 | 1.050 | 1.060 | 1.070 | 1.080 | 1.090 | 1.100 |
|---|---|---|---|---|---|---|---|---|
| 5 min | 5.5% | 5.0% | 4.6% | 4.2% | 3.8% | 3.5% | 3.2% | 2.9% |
| 10 min | 10.0% | 9.1% | 8.4% | 7.6% | 7.0% | 6.4% | 5.8% | 5.3% |
| 15 min | 13.7% | 12.5% | 11.4% | 10.5% | 9.6% | 8.7% | 8.0% | 7.3% |
| 20 min | 16.7% | 15.3% | 14.0% | 12.8% | 11.7% | 10.7% | 9.8% | 8.9% |
| 30 min | 21.2% | 19.4% | 17.7% | 16.2% | 14.8% | 13.5% | 12.4% | 11.3% |
| 45 min | 25.3% | 23.2% | 21.2% | 19.4% | 17.7% | 16.2% | 14.8% | 13.5% |
| 60 min | 27.6% | 25.2% | 23.1% | 21.1% | 19.3% | 17.6% | 16.1% | 14.7% |
| 90 min | 29.5% | 27.0% | 24.7% | 22.6% | 20.6% | 18.8% | 17.2% | 15.7% |
Tinseth utilization: the share of the alpha acids that ends up in the beer, by boil time and original gravity. IBU = utilization × alpha acid % × ounces × 74.9 ÷ gallons.
Whirlpool and hop stand IBUs
Alpha acids keep turning into bitter iso-alpha acids after the boil, just more slowly as the wort cools. The calculator counts a whirlpool addition as a shorter boil, scaled by the isomerization rate at its temperature. Below about 170°F (77°C) a hop stand adds very little bitterness, which is why brewers who want aroma without bitterness let the wort cool before they add the hops.
| Wort temperature | Isomerization rate vs. boiling | A 20 minute hop stand counts as |
|---|---|---|
| 212°F (100°C) | 100% | 20.0 min of boil |
| 205°F (96°C) | 72% | 14.3 min of boil |
| 200°F (93°C) | 56% | 11.2 min of boil |
| 190°F (88°C) | 34% | 6.8 min of boil |
| 180°F (82°C) | 20% | 4.1 min of boil |
| 170°F (77°C) | 12% | 2.4 min of boil |
| 160°F (71°C) | 7% | 1.4 min of boil |
From Malowicki and Shellhammer (2005). The calculator applies the same rule to every whirlpool addition.
Questions
What is an IBU?
An International Bitterness Unit is about 1 milligram of iso-alpha acids per litre of beer. A lab measures it; a calculator estimates it from the hops, the boil and the gravity. Most beers sit between 10 and 100 IBU.
How many IBUs is an IPA?
An American IPA is 40–70 IBU, a double IPA 60–100 and a hazy IPA 25–60. An American pale ale is 30–50, a German pils 22–40 and a hefeweizen 8–15 (BJCP 2021 style guidelines). The calculator highlights the styles that match your number.
Tinseth or Rager?
Tinseth for most homebrewing: it’s what most recipes, Brewfather and Brewer’s Friend use. Rager gives higher numbers for the same hops, so a recipe written with Rager will taste less bitter than its IBU suggests if you brew it with Tinseth numbers. Stick to one.
Do whirlpool hops add IBUs?
Yes, but less than boil hops. At 180°F (82°C) the isomerization runs at about a fifth of the boiling rate, so a 20 minute hop stand counts like about 4 minutes of boil. Near boiling, whirlpool hops add almost as much as a boil addition of the same length.
Do dry hops add IBUs?
Not in the calculation: dry hops never get hot, so their alpha acids don’t isomerize. Heavy dry hopping can add a little perceived bitterness from other hop compounds, and some lab tests pick it up, but the calculator counts dry hops as zero, as every standard formula does.
What is the BU:GU ratio?
The IBU divided by the gravity points (1.050 is 50 points). It shows how bitter a beer tastes against its malt. Around 0.5 is balanced, 0.3 or lower tastes malty, and 0.8 or higher tastes hoppy and bitter. A 40 IBU beer at 1.050 is 0.8; the same 40 IBU at 1.080 is 0.5.
Why does my beer taste less bitter than the calculator says?
The formulas are estimates. Bitterness is lost to trub, yeast and the fermentation itself, and it fades as the beer ages. Hops lose alpha acid in storage, so an old packet is weaker than its label. Measure your hops by weight, store them cold and sealed, and use this year’s alpha acid number.