Originally Posted by DogHouseMom
No. You are forgetting the seam allowances as you are talking about finished sizes.
Also, were you just planning on putting a border around each block? Or increasing each of the elements in the block to make the whole block larger?
If you want to add a border around each block to increase the FINISHED size from 10" to 12" then you need to add a 1.5" strip around each side.
10" + 1.5" + 1/5" less seam allowences (4 of them 2 each side of the 10" where joined to the strip and 1 each end of the strip to "finish" ) = 12" block
If you want to increase the size of each element within the block to make the whole block bigger then you need to work out the math for each individual element. If it's a 4 patch you can probably do this simply (because 4 is divisible by 2), but if it is a 3 or a 5 patch ... you will be working in other fractions.
What block are you trying to increase?
Ditto I was going to remind you of the seam allowances, but someone already has.