International bittering units (IBU) is easy to work out. Our IBU calculator easily calculates the bitterness of home brewed beer. The calculator uses both the Rager and Tinseth method of IBU calculation, so, depending on your ingredients, you can use the IBU from either method. Alternatively, use the the average of both methods to get a “middle of the range” IBU for your beer.
If you’re unsure whether to use the Rager or Tinseth method of IBU calculation, see below the IBU calculator for an explanation of each method as well as a more in depth discussion of calculating IBU.
If you’re unsure what an IBU is here, check out our article on what IBUs are. Otherwise just use the calculator above to calculate the IBU of home brew. If you’re curious about the method used, read further for various IBU calculation formulae.
The Rager Method and Tinseth Method of Calculating IBU
Both the Rager and Tinseth method of IBU calculation have their pros and cons, and are more appropriate for different types of brewing.
First of all, all mathematical methods of calculating the IBU of a beer are estimates only, the only accurate way to find the IBU of a beer is to measure it in a laboratory. Of course this isn’t possible in a home brewing set up, but mathematical methods are close enough to give you an idea to see if you’re on style.
The Rager Method, named after Jackie Rager, is thought to be a bit of an over estimate for finding IBU. This is because he is a bit confident with the utilisation of the hops in the boil. As can be seen in the IBU calculator, even at zero minutes, the hop utilisation is still worked out to be 5.1%.
Adding to that, the Rager method is generally best when using hop pellets (rather than fresh hops). So if you’re using hop pellets, the Rager method should be a good way to good.
The Tinseth Method, named after Glenn Tinseth is considered a little bit more accurate and will generally come out a bit lower than Rager’s numbers (but not always!). This is because Tinseth’s utilisation calculations are a little bit more involved. All in all, Tinseth took more time in working out the utilisation of hops, and admits to the empirical nature of his formula. So while the Tinseth Method should be relatively accurate, he encourages it to be modified to suit individual set ups.
And the Garetz Method of Calculating IBU
The Garetz Method is a little more conservative than the Tinseth Method, and is not presented in the IBU calculator above. This is because the Garetz Method is an iterative method of calculating IBUs. This means you have to guess the IBUs of a beer, do the formula, come to a closer result, and repeat. Honestly, our programming skills aren’t good enough for that, and asking users to guess an initial value takes away the point of a quick and easy IBU calculator!
The Garetz Method also takes into account utilisation and IBU loses from many different places, including from yeast, trub, and filters. As not all brewing set ups are the same, these loses add up and generally lead to a more conservative result. It also means that, since there’s so much variation in the average home brew set up, it’s all a bit of overkill!
So we’re not presenting it.
The Basic Concepts of Calculating IBU
The IBU of a beer relies on a few main factors: the amount of hops and their alpha acids; the utilisation of the hops; and the volume of the wort you’re making. Before we launch into how to calculate IBU yourself, it’s best to understand these three main factors.
Alpha acids are acids inside hops that are converted to iso-alpha acids when boiled and are what added bitterness to a beer. The more alpha acid in a hop and the longer it’s boiled, the more bitterness will be added to a beer. With this, more hops equals more alpha acid, and therefore more bitterness.
So the takeaway here when it comes to alpha acids is that the more of them found in a hop and the longer that hop is boiled will equal more bitterness in a beer.
The utilisation of hops or simply hop utilisation refers to how efficiently alpha acid is converted to iso-alpha acid. Basically how well the bitterness is extracted! This is both a function of time and the gravity of your boil. In regards to time, we already know that the longer a hop is boiled, the more bitterness will come out of a hop. So if you boil a hop for 30 minutes, you’ll convert 10-20% of the alpha acid to iso-alpha acid (depending on a few factors). One of these factors is the specific gravity of the boil! The lower the gravity of the boil, the better the utilisation of the hops. This is why the IBU calculator above asks for batch volume, boil volume, and target specific gravity. This is used to work out the boil gravity and therefore the utilisation.
The take away here is that the longer you boil a hop and the density of the boil affect how much bitterness comes out of that hop.
Finally, the volume of the wort comes into play because of its general diluting factor. A lot of calculating IBU is working out how many milligrams of alpha acids are extracted, and then dividing this by the volume of the batch (and doing a couple other things) to get the final international bittering units.
So the take away here is milligrams of alpha acid is diluted by the total batch volume for a final figure.
Calculating IBU Using the Rager Method
The Rager Method is by far the simplest to perform and the easiest to understand mathematically. The Rager Method formula is:
The amount of hops, the alpha percent, and the batch volume are decided by recipe. There are two factors in the above formula that need to be worked out: utilisation percent (% utilisation) and gravity adjustment (GA).
Where tanh refers to the hyperbolic tangent and boil time is the length of the boil in minutes.
The gravity adjustment is only applicable if the boil gravity is above 1.050. Otherwise it’s zero.
As stated, higher boil gravity amounts to a lower utilisation, so that’s why it’s thrown in there. However, it’s very general and obviously doesn’t take into account boil gravities of up to 1.049, which can actually change utilisation by up to about 4% according to the Tinseth Method.
Calculating IBU Using the Tinseth Method
The Tinseth Method is a little bit more involved as it the boil gravity is taken more into account in calculating hop utilisation. Because of this, it’s generally a little bit more conservative than the Rager Method. The Tinseth Method formula is:
The amount of hops, the alpha percent, and the batch volume are decided by recipe. Calculating hop utilisation comes from a multiplying to numbers, the Bigness Factor and the Boil Time Factor. These formulas were derived empirically by Tinseth.
Boil Time Factor
As mentioned the Bigness Factor and the Boil Time Factor were derived empirically by Tinseth to fit the data that he was finding on his equipment. The constants in these two factors can be changed to suit other home brew set ups if you’re keen on doing some experimentation.
And the IBU Calculator
Both the Rager and Tinseth Methods are used in the IBU calculator above. Depending on your preference or recipe, you can choose either method. Alternatively, the calculator also presents the average of both methods combined. Use any of them!
As stressed, both methods of calculating IBU are estimates only, but should give accurate enough numbers to know if you’re within style, recipe creation, or just seeing what you got. The only way to get the exact IBU of a beer is in a lab, which most home brewers don’t have access to!
So now that you can calculate the IBU of home brew, you’ll need to calculate the ABV of your home brew! But before you get brewing, you’ll have to calculate the strike water temperature for your grain mash. So check out our other calculators and explanations.