The best "guesstimate" is 1/4" per number increase. So you would get 1/2" front and 3/4" rear. In most cases it's still a WAG since every Jeep seems to be a little different and your other mods might impact the results as well.
I agree with Pressurized's guesstimate but keep in mind that the height of any corner on a JK can vary 1/4-1/2" just by they way the coils end up in their rest position. So measuring things to this degree can be fruitless.
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