I was hoping someone could help me out with my math. If I have a quilt that is 86x86 how much fabric should I buy? I want to order this online. As well as the fabric for the binding. I like wider bindings. It will be quilted by me. Thanks!

To make it simple buy 3 yds of 108 in. backing and have enough for binding and a little left over.

6 yards should be plenty--
36"x44" per yard---
5 yds- cut in half- sewn together- gives you a piece 90"x 88" (cutting it close here)
and leaves a yard for binding---
You only need about 22" for binding if using a 2 1/2" binding-
that leaves a little extra for fudge room- or to add to your stash.

Thanks for the help!

Here's a useful online calculator:
http://vrya.net/quilt/flash/QuiltCalc_Loader.html

I'll bet that leaves you short width wise. Most fabric isn't 44" anymore, it's more like 42" and you lose the selvedges so you end up with about 40".

I usually buy 108" fabric from www.fabric.com then figure out how many yards (36") from there. I don't like to piece the backs and I quite often use the backing for the binding as well.