Calulate Hops AAU

How do you calculate the correct amount of hops based on the AAU's ?
For instance, if a recipe calls for 1 oz Cascade @ 6.6% (21.4 IBU) , how do you know how much 7.2 Cascade to make it the same ?

Surely I am just overlooking a calculator here.

Oops! Bad math.

Here ya go:

How to Brew - By John Palmer - Hop Measurement

[FONT=Verdana, Arial, Helvetica, sans-serif]Calculating Alpha Acid Units
AAUs are a good way to state hop additions in your recipes. By specifying the amount of alpha acid for each addition, rather than e.g. 2 oz of Cascade, you don't have to worry about year to year variation in the hop. An AAU is equal to the % AA multiplied by the weight in ounces.

[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]For Example:
1.5 oz of Cascade at 5% alpha acid is 7.5 AAUs. If next year the alpha acid percentage in Cascade is 7.5%, you would only need 1 oz rather than 1.5 oz to arrive at the same bitterness contribution. [/FONT]

Click to expand...

So if 1 oz @ 6.6% AA = 6.6 AAU, then x x 7.2% AA = 6.6 AAU, so 6.6÷7.2 = ~0.92 oz.