IBU Calculator

Understanding IBU Calculations

International Bitterness Units (IBUs) measure the perceived bitterness in beer from hop alpha acids that are isomerized during the boil. The longer hops are boiled, the more alpha acids convert to iso-alpha acids, which provide bitterness.

Tinseth Formula

Developed by Glenn Tinseth, this is the most widely used formula in homebrewing software. It accounts for both the time-dependent utilization and the gravity-dependent utilization:

IBU = (W × AA × U × 1000) / (V × C)

Where utilization (U) = Bigness Factor × Boil Time Factor:

• Bigness Factor = 1.65 × 0.000125^(G - 1) where G is wort gravity
• Boil Time Factor = (1 - e^(-0.04 × t)) / 4.15 where t is minutes

Rager Formula

Jackie Rager's formula tends to give slightly higher IBU estimates. It uses a simpler utilization table and a gravity adjustment that kicks in above 1.050:

IBU = (W × U × AA × 1000) / (V × (1 + GA))

Where GA (Gravity Adjustment) = (G - 1.050) / 0.2 when G > 1.050, otherwise 0.

IBU Ranges by Style

• Light Lager: 5-15 IBU
• Wheat Beer: 10-20 IBU
• Pale Ale: 30-50 IBU
• IPA: 40-70 IBU
• Double IPA: 60-100+ IBU
• Stout: 25-45 IBU

BU:GU Ratio

The Bitterness Units to Gravity Units ratio helps determine the balance of your beer. A ratio below 0.5 suggests a malty beer, around 0.5-0.7 is balanced, and above 0.7 leans bitter/hoppy. GU is calculated as (OG - 1) × 1000.