stupid math question
 

I've decided to sew a bunch of leftover fabric to use as a backing for a quilt. If I have 12 inch blocks, they are really only 11 1/2 after they are sewn together, right? I'm just trying to figure out the easiest way to put all these things together to be the same size as the front. I HATE MATH!

Yes, if your square measures 12 inches unfinished, they will measure 11 1/2 inches when sewn together. You will actually want your back larger than the front when you layer the quilt.

We need to know how many blocks you have and if you intend to put in sashing before we can help with the size of the backing. if you have 12 inch blocks and putting 6 across would give you a width of 69.5 inches across.
(11.5 x 6 = 69 + .5 inch for the edge = 69.5.) To that I would add 6 inches = 75.5 inches which makes it easier to center the top on. Some people use less than 6 inches, and I have also, but prefer having the extra space.

You would do the same for the length as the width.

I never prepare the back until I have finished the quilt top, so I have the measurement of the actual top and not what I thought it would be.

You don't want to create too much additional bulk with your backing otherwise, when quilted, there may be some skipped stitches. You need to have the backing bigger otherwise it is almost impossible to line up the backing with the quilt top because the batting will be in the way.

To me, the totally math challenged quilter, all math questions are stupid...math is just plain stupid! LOL I know, I know, life as we know it couldn't exist without math! I am just numerically challenged! :D :D :D

Usually when people talk about 12" blocks they mean 12" finished size. 11.5" finished, (12"unfinished) would be very unusual.

My quilt top is 55 x 62. I'm just gonna start sewing blocks together for the back and see what I end up with! I've got 12 inch squares, 6 1/2 inch squares, random rectangles, etc. I'm trying to use up fabric. Thanks for your help. I'll be sure to make the back bigger.

I'm with you--there are no stupid questions, just stupid math! :)

If you are challenged with maths cut the blocks all the same size and join then even pins will so to the desired size. Measure if you feel brave . Or just lay another set out to match but back larger. It is easier to quilt if the back has a line of blocks and two large pieces of fabric . This reduces seams but gives a design on the back.

I am so glad to see others are mathematically challenged. I am always so embarrassed when i can't figure some things out. I always end up doing it the long way, the hard way or backwards :p I know i am no dummy and neither is anyone else here.