Bias Tape Calculator
Calculate continuous bias tape length from a fabric square, or the square size needed for a target length.
Reviewed by the ToolNestr Editorial Team — July 2026
How continuous bias tape is calculated
The continuous bias method cuts one long strip from a square of fabric by first joining two opposite edges into a tube, then cutting in a spiral along marked bias lines. Because the entire square's area ends up as one continuous strip of a fixed width, the total length is simply the square's area divided by the strip width — a bigger square or a narrower strip both produce more total length.
Working backward from a target length, the required square's area is the target length multiplied by the strip width, and the square's side length is the square root of that area.
This is the standard area-based formula for the continuous bias binding method used across dressmaking and quilting references; subtract a small amount for the tube-joining seam and trimmed ends in practice.
Worked example
A 36-inch square of fabric, cut into 2-inch-wide continuous bias strips.
Real-world context
Binding a quilt's curved edges, finishing a garment's neckline and armholes in one matching fabric, or edging a round tablecloth all rely on bias tape's ability to curve without puckering — knowing how much continuous tape a given fabric scrap can yield helps decide whether a leftover piece is enough for a project or whether more fabric needs buying.
Self-made bias tape in a specific matching or contrasting fabric is common when no commercial bias tape matches a project's exact color or print — calculating the needed square upfront avoids cutting and piecing fabric twice.
Common misconceptions
"Doubling the square size doubles the tape length." It roughly quadruples it. Since length depends on area, not side length, doubling a square's side length actually multiplies its area — and therefore the tape length — by about four times.
"Any diagonal cut counts as true bias." Only at 45 degrees. A cut at any other angle to the grain has less stretch than a true 45-degree bias cut, which is why continuous bias binding is specifically marked and cut at that exact angle.
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Frequently asked questions
What is continuous bias binding?
It is a method of cutting one long, continuous bias strip from a square of fabric by joining the two opposite edges into a tube before cutting, rather than cutting many separate short strips and sewing them together end to end.
Why is bias tape cut at a 45-degree angle?
Cutting on the true bias (45 degrees to the grain) gives the strip maximum stretch and lets it curve smoothly around necklines, armholes, and other curved edges without puckering, which a strip cut on the straight grain cannot do.
Does this formula account for seam allowance when joining the tube?
This gives the theoretical maximum continuous length from the square's area; in practice, subtract a small amount (a few inches) for the seam used to join the fabric into a tube and for trimming the tube's ends.
What strip width should I use?
Common finished bias tape widths are 0.5 inch (single-fold) and 1 inch (double-fold, before folding); cut the strip roughly 4 times the desired finished width to allow for folding both raw edges under.