Here is another wonderful and free website for calculating quilt yardage - Fabric Calculator.
I must admit I have a fun time at these web sites just planning out a quilt and playing around. There are two other tools I love to use. One is the EQ Software. I am a little out of the times as I still have the EQ5 (working very nicely, thank you), but there is a newer version. The EQ6. I dream of my first Baltimore Album Quilt!
Another quilting tool I find very helpful is the FabriCalc. I certainly let it do the math, while I just enter in the dimensions, types of blocks, and go from there. I do like to keep it in my tote for those shopping days! I place it up there with my rotary cutter!
Happy Sewing & Quilting!