How to Calculate IBU

A big part of recipe creation is calculating how much hops you need and when to add them to get the flavor you want. IBU (international bittering unit) is going to be your go to measurement as a home brewer.

Styles have IBU ranges, so you’ll want to try to fall in that range. However you don’t always have to. While IBU is a measurement of bitterness, the lower the number the less bitter. However a high number doesn’t 100% mean it’s going to be a super hoppy beer. If you have an excessively large grain bill, you’ll need higher IBUs to balance it out. Look at barley wines. They have really high IBU but aren’t necessarily bitter. They just need to be that high to counteract the really high maltiness of the beer.

So that all said, let’s do this.

The Hard Way

If you’re starting from scratch, we’ll have to determine the AAU (Alpha Acid Unit) then convert to IBU. Here’s how to do that:

First, calculate the Alpha Acid Units (AAUs)

AAU = Weight (oz) x % Alpha Acids (whole number)

Using AAUs, it’s important to note how long each addition will be in the boil. This has a huge impact on your final calculations (and of course flavor).

So to get there, we need to do one more minor calculation

IBU = AAU x U x 75 / V

U = Utilization

V = volume of boil

75 is a constant for the conversion of English units to Metric as IBU is technically in mg per liter.

Here’s chart for Utilization

Utilization as a function of Boil Gravity and Time

Gravity vs. Time

1.030

1.040

1.050

1.060

1.070

1.080

1.090

1.100

1.110

1.120

0

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

5

0.055

0.050

0.046

0.042

0.038

0.035

0.032

0.029

0.027

0.025

10

0.100

0.091

0.084

0.076

0.070

0.064

0.058

0.053

0.049

0.045

15

0.137

0.125

0.114

0.105

0.096

0.087

0.080

0.073

0.067

0.061

20

0.167

0.153

0.140

0.128

0.117

0.107

0.098

0.089

0.081

0.074

25

0.192

0.175

0.160

0.147

0.134

0.122

0.112

0.102

0.094

0.085

30

0.212

0.194

0.177

0.162

0.148

0.135

0.124

0.113

0.103

0.094

35

0.229

0.209

0.191

0.175

0.160

0.146

0.133

0.122

0.111

0.102

40

0.242

0.221

0.202

0.185

0.169

0.155

0.141

0.129

0.118

0.108

45

0.253

0.232

0.212

0.194

0.177

0.162

0.148

0.135

0.123

0.113

50

0.263

0.240

0.219

0.200

0.183

0.168

0.153

0.140

0.128

0.117

55

0.270

0.247

0.226

0.206

0.188

0.172

0.157

0.144

0.132

0.120

60

0.276

0.252

0.231

0.211

0.193

0.176

0.161

0.147

0.135

0.123

70

0.285

0.261

0.238

0.218

0.199

0.182

0.166

0.152

0.139

0.127

80

0.291

0.266

0.243

0.222

0.203

0.186

0.170

0.155

0.142

0.130

90

0.295

0.270

0.247

0.226

0.206

0.188

0.172

0.157

0.144

0.132

100

0.298

0.272

0.249

0.228

0.208

0.190

0.174

0.159

0.145

0.133

110

0.300

0.274

0.251

0.229

0.209

0.191

0.175

0.160

0.146

0.134

120

0.301

0.275

0.252

0.230

0.210

0.192

0.176

0.161

0.147

0.134

 

Applying

And now to get to the end result just use this formula:

IBU = [W(oz)*AA%*U*7489]/V

W = weight in oz

U = utilization

V = volume in gallons

Remotely

Note: If you have multiple hop additions add them to the equation like this

IBU = [W(oz)*AA%*U*7489 + [W(oz)*AA%*U*7489]/V

 

The Easy Way

Either let your brewing software take care of all the math for you or use one of these online calculators

Rooftop Brewing

Brewer’s Friend

Homebrewing.com

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