Bias Tape Length Calculator
Estimate how much continuous bias tape a square of fabric will yield, using the classic continuous-bias method.
How continuous bias tape works
Cut a square of fabric in half diagonally, sew the two triangles into a parallelogram along the straight (non-bias) edges, then draw lines parallel to the bias edge spaced one strip-width apart. Sew the parallelogram into a tube offset by one line, and cutting along the marked spiral produces one continuous bias strip.
Where the formula comes from
The total length produced is approximately the square's area divided by the strip width (side² ÷ strip width) — because the marked lines effectively slice the whole square's area into one long ribbon of that width. This is the standard estimate used in continuous-bias tutorials.
Buy a little extra
The formula gives a theoretical maximum. In practice you'll lose a bit of length to the seam allowance at the diagonal join and to trimming the tapered ends of the tube, so treat the result as an upper bound and add 10–15% to your fabric square size if you need a guaranteed minimum length.