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IBU (Garetz) Calculator

Estimate your beer's bitterness in IBU with the Garetz method.

How it is calculated

The tool takes a hop utilisation from a table of boil time against percent utilisation (for example 60 min = 31 %, 90 min = 34 %), interpolating between table points and capping at 34 % past 90 minutes. It then corrects for gravity and altitude:

IBU = (AA/100 × oz × 7489 × utilisation / gallons) / (GF × TF)

GF = 1 + (boil gravity − 1.050)/0.2 when gravity is above 1.050, otherwise 1; TF = 1 + (elevation / 550) × 0.02

AA is alpha acid in percent (above 0, at most 100), hop weight is in ounces, volume in US gallons, elevation in feet (0 to 30,000) and boil gravity a specific gravity between 0.98 and 1.20, such as 1.050. Values outside these ranges, or a blank field, give no result. Results show IBU with one decimal and the utilisation used. The tool handles a single hop addition, so add the IBU of each addition yourself.

Worked example

One ounce of 7 % alpha acid hops, boiled for 60 minutes in 5 gallons at boil gravity 1.050, at sea level.

Utilisation at 60 min = 31 %. The gravity factor is 1 (not above 1.050) and the elevation factor is 1.

IBU = (0.07 × 1 × 7489 × 0.31 / 5) / 1 = 162.5 / 5 = 32.5 IBU.

The same addition at 5,000 ft and boil gravity 1.070 would give about 25.0 IBU.

Try this example →

Common mistakes

  • Entering the hop weight in grams. The field is ounces, so 28 g must be entered as about 1 oz; typing 28 gives 910.1 IBU for this recipe.
  • Typing the batch size in litres instead of US gallons. A 19 L batch typed as 19 is read as 19 gallons, so the IBU comes out about 3.8 times too low (8.6 instead of 32.5 here).
  • Typing the gravity as 50 or 1050 instead of 1.050. Boil gravity outside 0.98–1.20 gives no result.
  • Leaving elevation blank. The tool needs a number, so enter 0 for sea level; a blank field shows no result.
  • Entering the alpha acid as a fraction (0.07 for 7 %). The field is a percentage, and 0.07 is accepted and quietly gives only 0.3 IBU.

About this calculator

The Garetz method estimates a beer’s bitterness in IBU (International Bitterness Units) using Mark Garetz’s hop utilization tables, but unlike the simpler Tinseth or Rager formulas, it also applies a gravity correction factor and an elevation correction factor — here a simple linear adjustment of about 2% less bitterness per 550 feet (roughly 170 m) of elevation, standing in for the lower boiling temperature at altitude.

Homebrewers use it to predict a finished beer’s bitterness before they ever brew it, and it’s particularly valued by brewers at high elevation, where the simpler formulas tend to overestimate how bitter the beer will actually turn out.

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