Bias Binding & Continuous Bias
Bias binding length from a rectangle, circle or measured edge, the strip width for single or double-fold tape, and the square that yields it as continuous bias.
How much binding an edge needs with your overlap, the strip width your tape size implies, the side of the square for the continuous-bias method, and the fabric to buy from your bolt width.
Example: A 36 × 48 in quilt with 10 in overlap needs 178 in of ½ in double-fold tape cut 2 in wide: an 18.9 in square (20.9 in with a 2 in margin) — 0.58 yd of 44 in fabric.
Area is length
times width.
How the binding length is found, how tape width becomes strip width, why a square of √(length × width) gives continuous bias, and what the area method leaves out.
Length and strip width
A rectangle needs its perimeter, a circle π × diameter, and a measured edge whatever you measured; the overlap you allow for joining the ends is added. Bias tape is named by its finished width: single-fold tape has both edges folded to the centre, so the strip is cut at twice the tape width; double-fold tape is then folded again down the middle, so the strip is four times the tape width. Enter the strip width directly when you cut to your own figure.
The continuous-bias square
A square cut on the diagonal, sewn into a tube with the seam offset by one strip width and cut in a spiral gives one continuous bias strip. The strip’s area is its length × its width, and the square’s area is its side squared, so the side is √(length × strip width). The margin you add covers the offset and the ends; the page assumes none.
When the square is too wide
If the square would be wider than the fabric, the page gives a full-width rectangle of the same area instead — the same arithmetic, length = area ÷ fabric width. Either figure is an area figure: a 45° cut and no loss at the joins are assumed, which is why the margin exists.
What the number does not settle
Strip width for a given seam and finished edge on a thick quilt sandwich, and the loss at each diagonal join when strips are pieced rather than cut continuous, are yours to allow for. For quilt binding cut across the grain in strips, see Quilt Binding. Inputs stay in your browser; the same anonymous usage counts as the rest of the site apply.