Bias Tape Length Calculator
Size the binding for an edge, work out the fabric square the continuous-bias method needs to produce it, or check how much tape a square you already have will yield.
1. Binding length for an edge
Cut this much binding
2. Fabric square for continuous bias
Square of fabric to start with
3. Or: tape obtainable from a square you already have
Continuous bias tape obtainable
The area behind the estimate
Once a square of fabric is turned into one continuous bias strip, the total length it yields is approximately the square’s area divided by the strip width — a 36in square cut into 2in strips can, in principle, unwind into around 648in of tape (36in² ÷ 2in), before any losses. The calculator applies a waste percentage on top of that raw figure to account for the tube seam and the trimmed ends, which is what keeps the estimate honest rather than optimistic.
Sizing the square works the same formula in reverse: multiply the length you actually need by the strip width to get the area, adjust for waste, and take the square root to get the side length to start cutting. Round up to a comfortable cutting size — a slightly bigger square costs little and saves a second trip to re-cut when a seam or a mis-cut eats into the first one.
Frequently Asked Questions
What is the 'continuous bias' method?
It's a way to cut one long bias strip from a square of fabric instead of many short diagonal strips you'd have to join end to end. The square is cut in half diagonally, the two triangles are re-joined offset by one strip-width to form a parallelogram, the long edges are sewn into a tube, and the tube is sliced in a single continuous spiral — producing one long bias strip in a handful of cuts.
What strip width should I cut?
For double-fold bias tape, cut about four times the finished width (a 1/2in finished tape is cut roughly 2in wide, since it folds in twice with a bit taken up by the folds). For single-fold tape, cut roughly twice the finished width plus a small seam allowance. Check your bias tape maker's size if you're using one — they're sold by the finished width.
Why does the calculator ask for a waste percentage?
The area math for the continuous method is a little optimistic in practice: the diagonal seam that forms the tube takes up some fabric, the very ends of the spiral are usually short offcuts, and real cutting is never perfectly efficient. A 10% waste allowance is a reasonable default; padded a bit higher if you're new to the technique.
Why does the binding length include ease and a join allowance?
Bias tape needs a small amount of slack to wrap around curves and corners without pulling tight or puckering, so cutting it exactly to the edge length usually comes up short in practice. The join allowance is the extra length needed to overlap and neatly finish the two ends of the binding once it's sewn on.
Educational tool only. Real yields vary with cutting accuracy and fabric grain; cut a little extra rather than exactly to the estimate.