Bias Binding Calculator

True bias is the 45-degree diagonal across woven fabric. At this angle, the fabric has maximum stretch and drape, which is why bias binding curves smoothly around necklines, armholes, and scalloped edges without puckering.

To find true bias, fold your fabric so the selvage aligns with the cross-grain (cut) edge. The resulting fold is a perfect 45-degree line. Cut along that fold and mark parallel lines from it for your strips.

Off-grain strips (cut even a few degrees away from 45 degrees) will not stretch evenly and will create ripples or tight spots on curved edges. Always use a clear ruler and rotary cutter for accuracy.

Always join bias strips on the straight grain, not on the bias. Place two strip ends right sides together at a 90-degree angle, forming an L shape. Draw a diagonal line from corner to corner across the overlap, sew on the line, then trim to a quarter-inch seam allowance and press open.

This diagonal seam distributes bulk across a wider area than a straight seam would, keeping the binding smooth and even. It also aligns the grain direction of both strips so they stretch consistently.

If you need a lot of binding (more than about 60 inches / 150 cm), consider the continuous bias tube method instead of joining individual strips. It produces one uninterrupted strip with no joins to worry about.

When binding reaches an outside corner (like a quilt corner or a square neckline), stop stitching exactly one seam allowance width before the corner. Backstitch, remove the piece from the machine, and fold the binding straight up at 45 degrees, then fold it back down along the next edge. This creates a neat diagonal miter on the front.

For inside corners (V-necklines, notches), clip the garment seam allowance almost to the stitching line at the corner point. This allows the fabric to open up and lie flat while you sew the binding in a straight line across the clip.

The 6 inches / 15 cm of extra strip length in the calculation accounts for the extra fabric consumed at each miter and at the start/end overlap where you join the binding to itself.