Bias Tape Calculator - Bias Strip Length and Strips from Fabric Width

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What Is Bias Tape, and Why Make Your Own?

Bias tape is a strip of fabric cut on the bias, which is the diagonal direction of the weave, at 45 degrees to the threads. Fabric cut on the bias stretches and curves, which is exactly what you need to bind a curved neckline, an armhole, or a rounded quilt edge. Straight-grain strips cannot bend around curves without puckering, but bias strips hug the curve smoothly.

Shop-bought bias tape comes in fixed colours and widths, and it rarely matches your project fabric exactly. Making your own takes a little time, but it matches perfectly, costs less, and lets you choose the exact width. This calculator tells you how much bias strip you need, how many strips to cut, and how much fabric those strips take.

How This Calculator Works

Start with the perimeter of the edge you want to bind. Measure around the neckline, the quilt edge, or the placemat, following the curve. The calculator adds ten percent extra for joins and easing around curves, because a strip that is exactly the perimeter will always come up short once you join pieces and ease them in.

Next it divides the total length by your fabric width to find how many strips you need. Each strip, cut diagonally, can be as long as the fabric is wide in practice for planning purposes, so the number of strips is the total length divided by the fabric width, rounded up. Multiply the strip count by your cut strip width, and you have the length of fabric to set aside.

How to Use It

Measure the edge carefully with a flexible tape, following every curve. Enter that perimeter, your fabric width, and the width you will cut each strip. A common cut width is 4 cm for tape that finishes around 1 cm wide when folded, but check your project: double-fold tape and single-fold tape need different cut widths.

Press Calculate. You get the total bias length including the ten percent extra, the number of strips, and the fabric length those strips need. Cut your strips on the true bias, join them with diagonal seams, press the seams open, and then fold or press the tape to its finished width before applying it.

Worked Example

A quilt edge measures 200 cm around. Add ten percent and the bias length is 220 cm. From fabric 110 cm wide, you need 220 divided by 110, which is 2 strips. If each strip is cut 4 cm wide, the fabric length needed is 2 times 4, which is 8 cm. So a strip of fabric just 8 cm long, cut across the full 110 cm width, gives you enough bias tape for the whole edge, with joins.

For a larger project, say a 500 cm edge with 140 cm wide fabric and 3 cm strips, the total is 550 cm, the strips are 4, and the fabric length is 12 cm. Small amounts of fabric go a long way when they are cut on the bias.

Tips for Beautiful Bias Binding

Cut accurately on the 45-degree angle. A strip cut even a few degrees off the true bias will stretch unevenly and pull to one side. Use a clear ruler with a 45-degree line, or fold the fabric corner to find the bias exactly. Join strips with diagonal seams that follow the grain, and press those seams open so the tape stays flat.

Pin generously around curves, and ease the tape rather than stretching it hard. Bias stretches, but overstretching makes it ripple after washing. Sew slowly around tight curves, and clip or notch the seam allowance where the curve is very tight.

Common Mistakes

The most common mistake is measuring the straight-line distance instead of the curved edge. A neckline that looks like 40 cm across a ruler may be 55 cm around the curve. Always measure with a flexible tape on the curve itself. Another mistake is cutting strips on the straight grain to save time. The binding will pucker at the first curve, and no amount of pressing will fix it.

A third mistake is forgetting joins. Each join eats a little length, and easing eats more. The ten percent extra in this calculator exists for exactly that reason. Do not set it to zero.

Frequently Asked Questions

Can I use leftover scraps for bias tape? Yes, if each scrap is wide enough for one strip length and you join enough strips. Short scraps mean more joins, but the tape still works.

What width should I cut? For single-fold tape, cut twice the finished width plus a small seam allowance. For double-fold tape, cut four times the finished width. Check your pattern for its exact figure.

Does bias tape work on straight edges? Yes, but it is not necessary there. Straight-grain binding is fine and uses less fabric on straight edges. Save bias tape for curves.

Please note: sewing results here are estimates and guidance only. Fabric, pattern and personal ease vary, so measure twice and buy a little extra.

Bias Tape Calculator – Bias Strip Length and Strips from Fabric Width