What is your bare minimum??
 

What is the bare minimum backing size you can get by with? Quilt top is 41". I currently only have one inch on the sides. Top and bottom are OK. The borders are 3.5 inches, so I can trim an inch off, which would give me a couple inches on the sides. I plan on SITD and echo quilting. Quilt has 5 10 x10 squares, and 2 18 x 10 squares, with 1 inch sashing between. The backing is perfect for the quilt. I've always had 4" or more overhang. Is this enough, or will I run into problems?

If you are quilting on your home machine you will be fine. I have gone as close as to have to trim a bit of boarder after quilting is done. Just go for it. As long as you can center it when you baste all will be fine

I have managed to quilt a quilt with only one inch extra arouind the edges - on my home machine - I had to be very careful with placement of the top, but it did work.

I also have managed to quilt with only one inch extra on my domestic machine. I think it helps to starch both top and backing before layering, and to spray baste (or glue baste). Both of those things help prevent fabric "creep". Using cotton batting (or 80/20) rather than polyester batting also helps prevent fabric creep, as the fabric sticks better to the cotton.

You'll be fine with the echo quilting. I don't know about SITD. We don't get along. The only time I've 'lost' backing was when I used a fleece back.

I use my domestic machine and mainly do meander quilting, and an extra 1" all the way around has been just fine. I do spray baste so that nothing shifts and make sure that everything is centered perfectly.

I think it will depend on your materials and how (well) you baste, as Prism99 has said. Slippery material like polyester is going slide more than cotton or wool. If it's cotton fabric with wool or cotton batting and it's well basted, I think you'll be fine. I don't know if cotton batting with a polyester scrim would be slippery or not.

When you've had 4" of overhand in the past, how much did you trim off after you were done? :)

Another thing that will add to the need for additional backing is the thickness of your batting. A thinner batting, like warm & natural or a thin poly will 'take up' much less than a puffier one. As mentioned, just baste well.

I have a margin of 1-2" of backing fabric. I mainly use hi loft poly batting and always use safety pins to sandwich.

Thanks for the replies! Top and back are all cotton. I'm using Warm and White batting, and I spray baste. I usually starch too, so I'll do that too. I'm going to trim the border a bit and go for it!