am I smarter than a 5th grader (nooooooo!!!!!!)
 

let's start this by saying I am not good at math. I need to figure how big my fabric square needs to be if the long side (across from corner to corner) measurement is 38". I need to figure four corners for a king size quilt and I can't for the life of me figure this out. If any of you know this formula, please help. I can quilt, add, subtract, multiple, and divide. Cannot do higher levels of math, who knew I would need formulas to quilt.?? lol

Sorry I can't help......worse person in math you ever saw. Am mathmetically challenged big time.
I'm sure there is someone on here that can help, though.

I don't quite understand your question. When I plan a quilt I use graph paper
or a spreadsheet. It's a lot easier with the latter because I can color and change
the size as I wish. Here's a screenshot of my current plan.

If the 38 inches is the diagonal of your square (which is how I read it) the sides of the square need to be 26 7/8 inch.


The formula is A squared plus B squared = the square root of the diagonal. Or, as this is a square, 2 times A times A (because A = B) = the square root of the diagonal. So if you take your 38 inches and square it (multiply 38 times 38) then divide that by 2 you have the number that if you find what multiplies itself to get that number that is the length of the side. Called the square root. Do not try this without a calculator or spread sheet. Confused? I don't blame you. It's harder to describe than to do. The number is 26 7/8 in this case.

tim in san jose

Why wouldn't just measuring down one side of the diagonal work? Wouldn't that give you 26 7/8 size square?

For future reference you can go to quiltville.com. Bonnie hunter has a chart for side and corner triangles. She has the formula to use and a nice chart

How did you come up with the 38" measurement? Is that "finished" or does it include the seam allowances? If you measured it by measuring the fabric, are you sure that you didn't stretch the fabric (especially if it was on the bias) during the measurement? Tim's method calculates the sides of the triangle that will complete your corners if your measurement is unfinished, but I'm not sure that it correctly takes into account the seam allowances. At any rate, please cut a triangle out of PAPER first and make sure it is the right size to be SEWN to your quilt top (realizing that there will be seam allowances on where the paper and the quilt top meet) before you start doing the same with your fabric.

I agree with the paper test sheet. You'll probably have to tape several pieces together. I would also make it slightly oversized (like an inch or so) and trim it down to square. Just MHO.

I always make them slightly larger since it is easier to trim than to add. I thought that is was 1.5 that you multiplied but maybe that is for setting triangles. If you don't use it, you lose your math skills. Those 5th graders were much smarter than any 5th grader I ever met.