# 🍺 Top-down Brew: IBU calculator

Purpose: For calculating hop bittering IBUs with the Rager and the Tinseth formulas

Hop weight (oz or grams)
Hop alpha acid percentage
Boiling specific gravity
Boil volume (gallons or liters)
Boil time in minutes

US units Metric units

Results:

## Notes:

An important invention for creating beer recipes was the development of methods for predicting hop bitterness. The present calculator estimates the International bittering units (IBUs) that will be produced from hops of a given weight, alpha acid percentage, and boil time. The models for this calculation are from Tinseth (more conservative) and Rager (more optimistic). For multiple hop additions you can keep entering the values and press the calculate button multiple times. The results will accumulate.

Homebrewers sometimes debate which approach is best: Tinseth, Rager, Garetz, or some other model. My view is that there is no single "best" model. The best approach is to understand the models and choose the model that matches your brewing situation. The Tinseth model was based on whole hops, so this is a good choice if you brew with whole hops. In contrast, fresh, pelleted hops have a higher utilization than whole hops, so the Rager model might be the best choice for pelleted hops. Using pellet hops in a strainer bag lowers the utilization, so the Tinseth model might be more accurate for bagged pellet hops.

It is important to understand that IBU calculators are a prediction of the IBUs in the same sense that a weather forecast is a prediction of what the weather will be like in the future. The calculated IBUs and actual IBUs measured from the beer may not be perfectly identical, just like a weather forecast can be off the mark. This is particularly important for IPAs that have massive amounts of hops, which might have measured IBUs that are substantially lower than the calculated value. It has been estimated that about 100 IBUs is the maximum level that can be reached. For example, the well-regarded Pliny the Elder double IPA from Russian River Brewing is about 100 IBUs, but the calculated IBUs for clones of this beer may be well over this amount.

For more information about the technical details of the Tinseth and Rager formulas, please see the Hop FAQ at realbeer.com or John Palmer's page on hop bittering calculations. See also Tinseth's bitterness calculator.