To finish a neckline or armhole with bias binding, sew a strip of fabric cut at 45 degrees to the grain to the raw edge, then either turn it completely to the inside as a narrow facing or wrap it around the edge so it shows as a trim. A strip cut on the bias stretches and bends, so it follows a curve smoothly where a straight strip would pucker. Strips 3.5 to 4 cm (1 3/8 to 1 1/2 in) wide cover most necklines and armholes.
This guide covers cutting and joining your own strips, both methods step by step, closing the binding neatly, and what to do when a bound neckline ripples or flips out.
Bias facing or bound edge: which finish do you want?
| Bias facing (turned inside) | Bound edge (visible) | |
|---|---|---|
| Seen from the outside | A line of topstitching about 8 mm (5/16 in) from the edge | A narrow band of binding, often in a contrast fabric |
| Seam allowance on the edge | Kept: the binding is sewn on the seam line | Trimmed off: the binding wraps the seam line |
| Strip width | 4 cm (1 1/2 in) for a 1 cm (3/8 in) allowance | 3.5 cm (1 3/8 in) for an 8 mm (5/16 in) binding |
| Typical use | Sleeveless tops and dresses, collarless blouses | Slip dresses, aprons, children's clothes, sheer fabrics |
| Difficulty | Easier | Needs a steady hand on the second pass |
Whichever you choose, staystitch the curves as soon as the pieces are cut: a line of regular stitches 3 mm (1/8 in) inside the seam line, in the part that the binding or the allowance will hide. It stops the neckline stretching while you handle it, which is the main cause of a gaping finish.
How to cut and join bias strips
Ready-made bias tape works, but strips cut from your own fabric match the garment and drape like it.
- Fold a corner of the fabric so the crosswise cut edge lies along the selvedge. The fold is the true bias, at 45 degrees to both.
- Press the fold lightly, cut along it, then rule lines parallel to the cut edge at your strip width with a long ruler and chalk.
- Cut the strips with scissors or a rotary cutter. For each opening, cut the length of the edge plus 5 cm (2 in).
- Join strips with a diagonal seam: lay two ends right sides together at a right angle, like an L, and stitch from corner to corner across the square where they overlap. The diagonal spreads the bulk; a straight join makes a lump.
- Trim the join to 6 mm (1/4 in), press it open and snip off the small points that stick out past the strip.
- Press the strip as your method requires, without pulling it: heat and a little stretch make it narrower and harder to sew.
As a guide, a 50 cm (20 in) square of fabric gives roughly 5 m (5 1/2 yd) of 4 cm strips once joined, enough for the neckline and armholes of several tops. The bias binding calculator works out the square you need for any length and width.
Method 1: a bias facing turned to the inside
This is the clean finish of most sleeveless tops: from the outside you see only a row of topstitching. The width rule is simple: cut the strip twice the seam allowance plus twice the finished width. With a 1 cm (3/8 in) allowance and a 1 cm finish, that is a 4 cm (1 1/2 in) strip.
Note: If your pattern has a 1.5 cm (5/8 in) allowance on the edge, either trim it to 1 cm before you start or cut 5 cm (2 in) strips. Otherwise too little binding is left after sewing to catch with the topstitching.
- Sew the shoulder seams and, for armholes, the side seams, so the edge forms a closed loop. Press the seams open.
- Press the strip in half lengthwise, wrong sides together.
- Start where the join will be hidden: the back shoulder for a neckline, the underarm seam for an armhole. Fold the first 1 cm (3/8 in) of the strip back on itself.
- Pin the strip to the right side of the garment, raw edges together. On inward curves like necklines and armholes, pull the binding very slightly as you pin, so it ends up a touch shorter than the edge: this draws the finished edge in to sit against the body.
- Stitch at 1 cm (3/8 in). When you come back to the start, lay the end over the folded beginning by 1.5 cm (5/8 in) and trim the rest.
- Trim the seam allowance to 5 mm (3/16 in) and clip into it every 1.5 cm (5/8 in) around the tightest part of the curve, without cutting the stitches.
- Press the binding and the allowances away from the garment, then understitch: sew through the binding and both allowances 2 mm (1/16 in) from the seam. This keeps the binding from rolling to the outside.
- Turn the binding completely to the wrong side, rolling the seam 1 to 2 mm toward the inside, and press with steam.
- From the right side, topstitch about 8 mm (5/16 in) from the edge, checking on the inside that you catch the folded edge of the binding.
Method 2: a visible bound edge
- Trim the seam allowance off the edge, so the raw edge is now the finished neckline. The neckline keeps its size, because the binding wraps the seam line instead of being sewn inside it.
- Make double-fold tape from a 3.5 cm (1 3/8 in) strip: press it in half lengthwise, open it, press both long edges to the center crease, then fold it in half again. Let one side sit about 1 mm wider than the other.
- Open the wider side and pin it, right side against the wrong side of the garment, raw edges together, pulling it slightly around inward curves as in Method 1.
- Stitch in the fold crease, about 8 mm (5/16 in) from the edge.
- Wrap the binding over the edge to the right side so its folded edge covers the first line of stitching by about 1 mm. Pin it, or glue-baste it with a water-soluble glue stick.
- Edgestitch from the right side, 1 to 2 mm (1/16 in) from the folded edge of the binding, and press.
Sewing the first pass to the wrong side means that the line that shows, the edgestitching, is the one you sew while looking at it.
Joining the ends neatly
For a perfectly flat join on a closed loop, leave 5 cm (2 in) unsewn at the start and at the end, open the strips, overlap them, mark where they meet and sew them together with a diagonal seam before you finish the stitching. The beginner-friendly alternative is to bind flat: sew the binding to the neckline before closing one shoulder seam (or one side seam for an armhole), then sew that seam straight across the binding ends and tack the seam allowance down.
What about knit necklines?
Knits are bound differently. The binding is cut across the fabric, in the direction of greatest stretch rather than on the bias, and cut about 10 % shorter than the neckline so it pulls the edge in. It is stretched evenly as it is sewn, with a narrow zigzag or a stretch stitch. See sewing knit fabrics on a regular machine for the full method.
Common problems and how to fix them
- The binding rolls to the outside. It was not understitched, or the seam was not rolled to the inside when pressing. Understitch, then press again from the inside.
- The neckline ripples or stands away from the body. The edge stretched while you sewed, or the binding went on with no tension. Unpick, staystitch the edge, steam it back to shape and sew the binding a little tighter on the inward curves.
- The binding pleats or puckers. It was pulled too hard, or pulled on an outward curve, which needs the binding eased in instead. Unpick the puckered section and sew it again with less tension.
- The back of a bound edge is not caught. Both halves of the tape were the same width. Make the back half 1 mm wider and pin or baste before edgestitching.
- A lump at the join. The strips were joined with a straight seam or overlapped too much. Use a diagonal join trimmed to 6 mm (1/4 in).
- Not enough binding to topstitch. The strip was too narrow for the seam allowance. Use the width rule: twice the allowance plus twice the finished width.