it really really depends on the size of the quilt, the density of the quilting, the thickness of your sandwich...if i were going to try it with the 500 yard spools i would get 5 or 6 of them just to make sure i had enough...with the cones i would think 2 would be plenty, one to use for bobbins, one for on top. once you do one you will have a much better idea on how much you use...you and i could both quilt the same quilt with the same thread and both use a different amount, so it is really hard for someone to tell you you will need 2500 yards, or whatever. it will also make a difference if you are new to quilting and find you have to take any stitching out...that's more thread...so, get more than you need at first. the left over thread can always be used for piecing later.