Figuring out hop amout of diffent strengths

[g_rath]

I have been "winging it" with my hop calculations. What is the formula for figure out the correct amount of hops of a different strength?
For example: recipe calls for 1oz of 5% aa hops and I bought hops at 6%. How much do I need? I know I learned this in high school but damn if I can remember exactly how to do it. Thanks.
Ps. The SWMBO and I have a "discussion" going over this

 

[libeerty]

If you multiple the ounces by the AA, that should give you a target. Then take the AA of the hop you have and divide that into your target number, should give you the ounces you need, right? Few Double IPAs deep though..

 

[amandabab]

If you multiple the ounces by the AA, that should give you a target. Then take the AA of the hop you have and divide that into your target number, should give you the ounces you need, right?

yup. charlie's oldschool HBU system.

1oz x 1%AA @60min = 1 home bittering unit for a 5 gallon batch

 

[KeyWestBrewing]

yup. charlie's oldschool HBU system.

1oz x 1%AA @60min = 1 home bittering unit for a 5 gallon batch

Ive never read his book... How many HBU= 1 IBU?

 

[amandabab]

Ive never read his book... How many HBU= 1 IBU?

The 2 aren't directly linked.
Its for converting 1 known quantity of hops to another

 

[KeyWestBrewing]

Interesting

 

[RainyDay]

You're over thinking it. When you think you have enough, add more.