IBU Calculator
Estimate how bitter your beer will be before it is even brewed. Using the Tinseth method, enter your batch size, gravity, and up to three hop additions to get total IBUs and the bitterness-to-gravity balance.
Use the post-boil batch volume and the average boil gravity for the closest estimate.
Leave a row's weight at 0 to skip it. Flameout and dry hops add little measured bitterness in this model.
Formula & how it works
For each addition, the alpha-acid concentration is weight(oz) × alpha% × 7490 ÷ volume(gal) in mg/L. Utilization is bigness × boil-time, where bigness = 1.65 × 0.000125^(gravity − 1) and boil-time = (1 − e^(−0.04 × min)) ÷ 4.15.
IBUs from an addition are utilization × concentration, and the batch total is the sum. BU:GU is IBU ÷ gravity units, where gravity units are the last two digits of the gravity.
Worked example
In a 5 gallon batch at 1.050, one ounce of 6% hops boiled 60 minutes gives about 21 IBU on its own. Add half an ounce of the same hops at 15 minutes (~5 IBU) and the batch lands near 26 IBU, for a BU:GU of about 0.52 — a balanced bitterness for the gravity.
Designing bitterness
Time and gravity drive utilization
Longer boils extract more of the alpha acids, which is why the 60-minute addition does most of the bittering work while late additions contribute more aroma than measured IBUs. Higher-gravity worts extract slightly less, so a strong beer needs a touch more hops to hit the same bitterness as a lighter one.
Balance, not just a number
Bitterness reads differently against different amounts of malt. The BU:GU ratio captures that: the same 30 IBU feels sharp in a light lager and mellow in a rich amber. Aiming for a ratio that suits the style is often more useful than chasing a specific IBU figure.
Calibrate to your system
Every brewery extracts hops a little differently depending on boil vigour, whirlpool practice, and hop form. Use this to compare recipes and get in the right range, then trust your palate — after a couple of batches you will know whether your setup runs a little above or below the model and can nudge accordingly.