This calculator can take the basic values from standard recipes (weight, time, alpha acid percentage) and easily convert these to IBU percentages for use in a flex recipe.

The IBU calculations are based upon the Tinseth formula. A small improvement upon the Tinseth formula is that aroma hops (defined as less than 2 minutes of boil) are assumed to have a utilization of 5%. The IBU calculations estimate boil volume and gravity for a 15% per hour boil off rate.