That 5/8 yard is the rounded-up shop cut for 2 1/2 inch strips on 42 inch fabric.
Measure after quilting. The sewing walkthrough is how to bind a quilt. For the rest of this size see how much fabric for a twin quilt.
A worked answer
Double-fold binding for a 70 by 90 inch twin — strip count, yardage, and a card you can change.
That 5/8 yard is the rounded-up shop cut for 2 1/2 inch strips on 42 inch fabric.
Measure after quilting. The sewing walkthrough is how to bind a quilt. For the rest of this size see how much fabric for a twin quilt.
For a 70 by 90 inch quilt, cut 2 1/2 inch strips. The perimeter is 330 inches, plus 10 inches for joins. That is 9 strips from 42 inch fabric, which comes to 5/8 yard.
Measure the quilt after it is quilted. Binding cut for the pattern ideal size is often short of the quilt you actually have.