My brain can't math today....
 

So, I wanted to do a 4 patch block that finished out as 7.5 inches...and for the life of me, I can't work out the math of how big I need to cut my squares...I was never good at math, but I swear, the more life I have behind me, the dumber my brain gets where math is concerned...

Each square should be cut 4.25"; the finished size will be 3.75". 3.75 x 2 = 7.5.

I love people who can do math!!!

A lot of times I bring out a sheet of paper to figure something like this out. Cut the paper the size of the finished square, fold it into the required number of squares, then cut out and add seam allowance.
I started quilting in the mid-80's by drafting my patterns, drafting comes in handy to create blocks or quilts as needed.

It happens to everyone. If you can, draw out the finished block on paper and cut the pieces apart. Then add the seams and measure. It takes more time and more work - but - it also gets you past the brain glitch!!!!!!!

Bonnie Hunter's website has a calculator that will give all kind of helpful information. I am going to include the website address here as well as one other and the last one is an app for your phone quiltville.com myquilter.com and the is Robert Kaufman, I just typed in quilting calculator in the play store search. These have come in very handy for me many times, the myquilter one the lady at the quilt shop suggested it as it is what they use in the store.

7.5 finished is a very unusual size for a finished block. When we say finished that is the size of the block once it is sewn into the quilt. 7.5 is a more common UNfinished size (which is what the block would measure once completed but before it is sewn into the quilt)

So if 7.5 is correct that means before your block is sewn into the quilt it will measure 8" and Irish NY sizes are correct. But if you meant to say 7.5 unfinished size then your 4P squares need to measure 4" each.

I think that sometimes its not that we are dumb. Sometimes we just overthink things. I'm so bad about that.