About the Beer IBU Calculator
This beer IBU calculator estimates how bitter your homebrew will be, in International Bitterness Units, from your hop schedule. Enter up to four hop additions — weight, alpha-acid percentage and how many minutes each one boils — along with the batch volume and the gravity of the wort in the kettle. It returns the total IBU, each addition’s contribution and the BU:GU ratio that tells you how bitter the beer will taste relative to its malt sweetness.
Bitterness comes from alpha acids in hops, which only dissolve in wort after they are isomerised by boiling. Long boils extract more, and denser (higher-gravity) worts extract less, which is why a 60-minute addition delivers several times the bitterness of a 5-minute one. The calculator uses Glenn Tinseth’s formula, the default in most brewing software.
Use the post-boil volume going into the fermenter and the average boil gravity for the best estimate. Real IBUs also depend on kettle geometry, whirlpool time and fermentation, so treat the number as a recipe-design guide — typical ranges are 8–20 IBU for wheat beers, 20–40 for pale ales and 40–70+ for IPAs.
With the default inputs, the estimated bitterness is 54.7 IBU. Change any value above to recalculate instantly.
How to use the beer ibu calculator
- 1Enter the post-boil batch volume and choose gallons or litres.
- 2Enter the boil gravity (use your OG if you do not know it).
- 3For each hop addition, enter weight, alpha-acid % from the package and boil minutes.
- 4Tick pellet hops if you want the common 10% pellet bonus.
- 5Adjust weights or times until the total IBU fits your style.
Formula and method
Glenn Tinseth’s model estimates the fraction of alpha acids that end up as dissolved iso-alpha acids (utilization, U). The “bigness” factor 1.65 × 0.000125^(G − 1) reduces utilization in denser wort, and the boil-time factor (1 − e^(−0.04t)) ÷ 4.15 rises quickly at first and levels off after about an hour, reaching roughly 23% for a 60-minute boil at 1.050.
The milligrams per litre of alpha acid added are AA × weight in grams × 1000 ÷ volume in litres. Multiplying by U gives IBUs (1 IBU = 1 mg/L of iso-alpha acid). Many brewers add about 10% for pellet hops, which release alpha acids more readily than whole cones. BU:GU divides total IBU by gravity points ((G − 1) × 1000) to describe the bitter-sweet balance.
- AA
- Alpha acid fraction (6% = 0.06)
- W_g
- Hop weight in grams
- V_L
- Post-boil volume in litres
- G
- Boil gravity, e.g. 1.050
- t
- Boil time in minutes
Worked examples
5-gallon American IPA
At 1.050 a 60-minute boil gives about 23.1% utilization. One ounce of 12% hops in 5 gallons (18.9 L) adds 179.7 mg/L of alpha acid, or 41.5 IBU. The 15- and 5-minute additions add about 9.4 and 3.8 IBU, for roughly 54.7 IBU total — a BU:GU near 1.1.
20 L batch in grams with pellets
At 1.060 utilization drops to about 21.1% for 60 minutes; with the 10% pellet bonus it is 23.2%. 25 g of 10% hops in 20 L is 125 mg/L of alpha acid, giving 29.0 IBU; 30 g of 6% hops for 10 minutes add 7.6 more.
Single 60-minute bittering charge for a light lager
Three-quarters of an ounce of 4% hops boiled 60 minutes in 5 gallons at 1.045 gives about 10.8 IBU, a BU:GU near 0.24 — gently bitter and malt-forward.
Frequently asked questions
What is a good IBU for a pale ale or IPA?+
American pale ales usually fall around 30–50 IBU, American IPAs 40–70 and double IPAs 60–100+. Wheat beers and light lagers are typically 8–20 IBU, and stouts 25–45.
Why does boil gravity affect IBUs?+
Dense, sugary wort dissolves less of the isomerised alpha acid, so the same hops give fewer IBUs in a strong beer. Tinseth’s formula captures this with a bigness factor that falls as gravity rises.
Should I use pre-boil or post-boil volume?+
Use the volume of wort at the end of the boil (what goes into the fermenter plus kettle losses), because IBU is a concentration. Using a larger pre-boil volume underestimates bitterness.
What is the BU:GU ratio?+
It is total IBU divided by gravity points (for 1.050, 50). Around 0.5 tastes balanced; below about 0.3 is malty, above 0.8 is distinctly bitter, as in most IPAs.
Do late and dry hops add IBUs?+
Dry hops add almost no measured IBU, though they add perceived bitterness and aroma. Flameout and whirlpool hops add some IBU while the wort stays hot, which the basic Tinseth formula ignores.