So, I'm very, very new to quilting, and I'm sure this is a very elementary question. But I still need help!

I'm doing a T-shirt quilt. I was trying to make my squares 14" in addition to the seam allowance. Well, that's already gone because I have such trouble cutting precise squares! That's my question. How do I make sure I get exactly the size I need? Some of the sides will be sloped a little because I must've moved a little. I understand now why everything needs to be an exact measurement. I'm assuming I can just bring down the measurement a little, just as long as they are all the same size. But I can't get them all the same size! I am surely not cutting anymore until I figure it out, because I would hate to mess up beyond repair. I have a 12" by 18" mat, and a 18" ruler.

I know most of you are way beyond me, so thanks for answering my question! :-)

Have you stabilized the tee-shirts with something, interfacing or whatever? It seems like cutting a knit might be easier after it is stabilized.

I like to do my cutting on the floor. If your knees allow, that might be part of the answer. I put a knee on the ruler and it helps keep it firmly anchored where I put it.

Maybe you can use some of the scraps of tee shirts already cut to practice cutting some more on?

I was going to suggest the stabilizer, too. That would make a big difference in cutting

and you don't want a long skinny ruler, the fatter the better, 6X18 would be real good, or even a big square one

if you don't want to use stabilizer soak your t-shirts in starch and let them dry then iron the snot out of them. Then get a square ruler or l-shaped ruler and that will help getting them squared up properly. I would also suggest maybe getting a larger mat so that you can just turn the mat or walk around the mat as you cut. that could be part of the problem. the mat is not large enough to accommodate a 14" square. I had to get a real cutting mat when I started making quilts. I had been using a 6 1/2" x 12" cutting mat. it will make a world of difference in the cutting.

They really need to be stiff...

I have made about 8 T-shirt quilts. I use my 12 1/2" square ruler and cut my shirts out using that. I do not move the ruler at all. Basically I contort myself to cut out the square so I don't have to move the ruler. I don't stabalize or starch when cutting but as soon as I cut the T-shirt square I have my ironing board right behind me so the cut square goes on the ironing board and I have a 12 1/2" fusible interface ready to immediately put on my cut T-Shirt. I agree with the others, you need a bigger cutting mat too, at the very least it would make things much easier for you and result in more accurate cuts.

My only addition is if you are having problem with the ruler slipping, I have added little circles of sandpaper to the underside of my ruler. It helps keep it from sliding if that is an issue. You can find them at the sewing store or make your own.

I'd get the iron on stabilizer and get it ironed on BEFORE trying to cut. I've tried marking on knits before, and even that can pull a knit out of line.

there is no rule that says the squares all have to be the same size. You can add strips of coordinating fabric to the smaller blocks to bring them up to the size of the larger ones..might even add some interest to the quilt to have some variation in the sashing.