This is tough though, cause I'd sure like to know how much fabric I need to buy when planning a quilt.
i do the math quickly in the shop (i carry a small calculator)
for example - 40" X 40" finished size wall hanging
if you cut selvage to selvage, you're gonna get about 40" of length per cut. so one cut would do each side of this wall hanging (for a border). so whatever your width of border is going to be, take that times four. a 3" border x 4 = 12". then add a another 3" for cutting errors, etc. = 15"
same thing with binding, except you need to add a couple of inches to each side for calculating purposes if you mitre the corners and for overlap to make the final seam. i most always use 2.5" strips for my bindings. so if you add up all four sides of the unbound quilt 4 X 40" = 160". add 8" for corners/overlap. 168" divided by 40" (width of your fabric) = 4.2 strips that you will need to get around that quilt. then take the 5 (4.2 rounded up) strips X 2.5" per strip = 12.5" of fabric.
so for the 3" border and binding for a 40" wallhanging i would want to buy 1 yard of fabric to get the 27.5" i need. and i would have a few inches extra for cutting errors/stash.
keep in mind that these numbers are inflated because the FINISHED size is 40" by 40" which i used to calculate the borders. also, most fabrics you'll get 41-42" from a cut, but i use 40" to make SURE i have enough.