Which IBU formula does this calculator use?

The calculator uses the Tinseth method for boil additions. Whirlpool estimates apply a temperature factor informed by Malowicki (2005).

Do pellet hops yield more bitterness than whole hops?

Yes. A 10% utilization bump is commonly applied to pellet hops compared to whole/leaf hops.

What gravity should I use?

Use the wort specific gravity during the boil (commonly the post-boil OG for most homebrew calculators).

Does dry hopping add IBU?

Dry hopping adds minimal measurable IBU via polyphenols but no additional isomerized alpha acids; it is generally excluded from IBU calculations.

How accurate are whirlpool IBU estimates?

They are approximations. Utilization below boiling is temperature- and time-dependent; the temperature factor provides a reasonable estimate but not a laboratory measurement.

Which volume should I enter?

Enter the final volume into the fermenter (liters or US gallons). Tinseth uses final volume when computing mg/L of iso-alpha acids.

IBU (International Bitterness Units) Calculator

Authoritative Content Ecosystem

Data Source and Methodology

Authoritative Sources

Tinseth (1997) — The Relative Utilization of Alpha Acids From Hops (utilization model widely adopted by brewers). Reference: Glenn Tinseth. Link: https://www.tinseth.com/
Malowicki (2005) — A Study of Factors Affecting the Formation of Iso-Alpha-Acids During Wort Boiling (temperature/time kinetics for isomerization). DOI: 10.1094/ASBCJ-63-007. Abstract: ASBC Journal

All calculations are strictly based on the formulas and data provided by this source.

Specifically, boil additions use the Tinseth utilization equation. Whirlpool/steep estimates adapt Tinseth with a temperature factor informed by Malowicki’s kinetics. Pellet hops apply a commonly accepted 10% utilization increase versus whole/leaf hops.

The Formulas Explained

Tinseth utilization (boil):

U = 1.65 \times 0.000125^{(G - 1)} \times \dfrac{1 - e^{-0.04\,t}}{4.15}

IBU contribution (per addition):

\mathrm{IBU} = \dfrac{w_g \times 1000 \times \alpha \times U}{V_l}

Pellet vs. whole adjustment:

U_{\text{adj}} = U \times f_{\text{form}}, \quad f_{\text{form}} = \begin{cases} 1.10 & \text{pellet} \\ 1.00 & \text{whole/leaf} \end{cases}

Whirlpool/steep temperature factor:

U_{\text{whirlpool}} = U \times f_T(T), \quad f_T(100^{\circ}\mathrm{C}) \approx 1.00,\; f_T(90^{\circ}\mathrm{C}) \approx 0.55,\; f_T(80^{\circ}\mathrm{C}) \approx 0.32,\; f_T(70^{\circ}\mathrm{C}) \approx 0.18,\; f_T(60^{\circ}\mathrm{C}) \approx 0.08

Glossary of Variables

G: Specific gravity of the wort during boil (e.g., 1.050).
t: Time in minutes the hops are exposed at the specified conditions (boil or whirlpool).
U: Tinseth utilization (dimensionless), fraction of alpha acids isomerized and retained.
w_g: Hop weight in grams for a single addition.
α: Alpha acid fraction (e.g., 12% → 0.12).
V_l: Final batch volume in liters.
f_form: 1.10 for pellet hops; 1.00 for whole/leaf hops.
f_T(T): Whirlpool temperature factor (dimensionless) scaling utilization below boiling.
IBU: International Bitterness Units, mg of iso-alpha acids per liter of beer.

Worked Example

How It Works: A Step-by-Step Example

Goal: 20 L batch, wort gravity G = 1.050.

Hop A (pellet): 20 g, α = 12%, boil 60 min.
Hop B (pellet): 15 g, α = 8%, whirlpool 20 min at 80°C.

1) Tinseth utilization for Hop A:

U = 1.65 \times 0.000125^{(1.050 - 1)} \times \dfrac{1 - e^{-0.04 \times 60}}{4.15} \approx 0.246

Pellet adjustment: U_{\text{adj}} = 0.246 \times 1.10 \approx 0.271

IBU(A): \dfrac{20 \times 1000 \times 0.12 \times 0.271}{20} \approx 32.5

2) Whirlpool factor at 80°C: f_T(80^{\circ}\mathrm{C}) \approx 0.32

Base U at 20 min: U \approx 0.105 → Pellet-adjusted: 0.105 \times 1.10 = 0.116 → Whirlpool-adjusted: U_{\text{whirlpool}} \approx 0.116 \times 0.32 = 0.037

IBU(B): \dfrac{15 \times 1000 \times 0.08 \times 0.037}{20} \approx 2.2

Total IBU ≈ 34.7

Frequently Asked Questions (FAQ)

Which utilization model do you use?

Boil IBUs are calculated using the Tinseth method. Whirlpool/steep IBUs apply a temperature factor guided by Malowicki’s kinetics.

How do pellet vs. whole hops affect IBUs?

Pellet hops are modeled with a 10% higher utilization than whole/leaf hops due to better surface area and extraction.

Do I use pre-boil or post-boil gravity?

Use the gravity representative of the boil—most homebrew calculators default to post-boil OG, which is a practical approximation.

Can I include dry hop additions?

Dry hops provide aroma and some polyphenol bitterness but do not significantly raise iso-alpha acids; they are typically excluded from IBU calculations.

Why don’t different calculators match exactly?

Differences in utilization curves, temperature assumptions for whirlpool, volume definitions, and rounding can produce small variations.

What about boil-off or trub losses?

Tinseth’s core formula uses final volume. Losses indirectly affect calculated IBUs by changing the final concentration; enter the fermenter volume for best consistency.

Is there a max IBU?

In practice, solubility and sensory thresholds limit measurable IBUs. Extremely high hopping rates may not translate linearly into higher IBU readings.

Authorship and Review

Tool developed by Ugo Candido. Content verified by the CalcDomain Brewing Science Editorial Board.
Last reviewed for accuracy on: September 12, 2025.