Whether you're using a quilt kit or starting without a pattern, here's a helpful guide to which quilt sizes fit which size bed.
Crib quilt 34" by 52"
Twin-bed-sized quilt 70" by 90"
Double-bed-sized quilt 85" by 108"
Queen-sized 90" by 96"
King-sized 108" by 96"
California-King-Sized quilt 114" by 120"