How to Make Bias Binding

A bias binding calculator answers one question: how big a square to cut and how many yards of tape it yields. This guide answers the other half. Once the strips are cut, how do you turn them into a binding that wraps a raw edge, squares a corner, and rounds a curve without a single pucker? Making bias binding is really two jobs, cutting and pressing the tape and then sewing it on, and most of the trouble makers run into lives in the second. The bias binding calculator handles the measuring; what follows is the needle-and-thread work it leaves off.

Why Bias, and Where the Calculator Leaves Off

Bias is the diagonal of a woven fabric, the line that runs at 45 degrees to the selvage. Cloth cut on that true diagonal behaves differently from cloth cut along the grain: it has give, it frays far less than a cross-grain edge, and it can be coaxed around a curve. That last property is the whole reason bias binding exists. A strip cut on the straight grain is rigid across its width and fights any curve you ask it to follow, while a true-bias strip stretches along its outer edge and settles along its inner one, so it hugs a neckline or a scalloped quilt edge where a straight strip would buckle.

The cutting itself is a geometry problem, and it is the calculator's job rather than this guide's. In short, you cut a fabric square in half on the diagonal, seam the two triangles into a longer parallelogram, then mark and cut one continuous spiralling strip from it. One figure is worth carrying over before you sew. The square's area divided by the strip width gives a theoretical maximum, not the bias you actually end up with: you lose roughly half an inch off each side to the joining seam, and the diagonal joins eat another ten to fifteen inches over a long run, so cut the square a size up rather than to the wire. To work out how much fabric the square needs in the first place, the fabric yardage calculator estimates it from your project dimensions.

Single-Fold or Double-Fold: Pressing the Tape

Before any binding goes onto a project, the cut strip has to be pressed into shape, and there are two shapes to choose between. The choice decides how the binding looks and how much edge it can cover, so press a test length and look at it before committing the whole strip.

Single-fold tape has both long raw edges pressed in to meet at the centre. It lies flat, it is thin, and it suits lightweight jobs: an inside facing, a casing, a hem on fine fabric where a thicker fold would show as a ridge. Double-fold tape takes that single-fold strip and folds it once more down the middle, so the two pressed edges sit together and the strip wraps right around a raw edge to cover it on both faces. Double-fold is the durable one, the version that encases a quilt edge or a bag opening that will be handled and washed.

The cut width follows the finished width you want, by a rule of thumb rather than an exact law. For single-fold, cut about twice the finished width; for double-fold, cut about four times. A half-inch double-fold binding, then, starts life as a strip cut close to two inches. Treat those multiples as a starting point: many makers shave an eighth of an inch off when making the tape so the pressed edges meet cleanly instead of overlapping into a ridge, and a binding loses a touch more width to the turn of the cloth as it wraps a thick edge. One naming trap is worth stating plainly, because two conventions are in circulation. This guide sizes tape by its finished folded width, so a half-inch double-fold finishes at half an inch. Some packaged tapes are labelled by their flat single-fold width instead, so a spool described the same way can finish at half that. Read the size as the finished folded width, and a strip cut at four times that width comes out right.

A bias tape maker, the small metal funnel the strip feeds through, folds the edges in for you as you press, and it is worth having if you make tape often. Whichever way you press, press firmly and let the strip cool before you move it, because a warm fold opens up again. How wide a strip you can cut in the first place is capped by the bolt, and our guide to standard fabric widths sets out how much usable cloth different fabrics give you.

Attaching Binding to a Straight Edge

With the tape pressed, attaching it is a two-pass job: stitch one side down by machine, wrap the binding over the raw edge, then secure the other side. Work a straight edge first, since corners and curves build on the same motion, and pin or clip the length before you start so nothing shifts under the foot.

1. Open out one fold of the tape and lay it on the front of the work, right sides together, raw edges aligned.
2. Stitch along that first crease line, the fold you opened out, keeping the needle in the crease the whole way.
3. Fold the tape up and over the raw edge to the back, so the centre fold sits on the edge and the remaining pressed fold covers your stitching line.
4. Secure the back edge: by machine, stitching in the ditch from the front so the stitches sink into the seam line, or by hand with a slipstitch that stays invisible.

Two details decide whether the back comes out clean. The seam allowance is not a fixed number, because you stitch in the first crease, so the allowance is the width of that fold, and wider tape means a wider allowance. Quilt binding is the exception that quotes a number: a quilt's doubled, or French, binding is one strip folded in half with both raw edges caught in the seam, sewn at a flat quarter inch to match the piecing, with no fold to open. That quarter inch belongs to the quilt method, not to bias tape in general. The second detail is which side you secure last. Commercial double-fold tape is folded slightly off-centre, one side wider than the other, so put the wider side underneath and attach the narrower side first; when you then topstitch from the front, the wider back fold is sure to be caught. That one habit cures most of the misery of stitching that misses the binding on the back. Choosing between machine and hand is a trade: machine stitching is fast and stands up to washing, while hand stitching is slower but nearly invisible and right for an heirloom piece. For a whole quilt's worth of edge, the quilt binding calculator works out the yardage before you start.

Turning a Corner with a Mitre

An outward corner is bound with a mitre, a neat 45-degree fold that lets the binding turn ninety degrees and lie flat on both sides. The fold is simple once the timing is right, and the timing is the part to get exactly so.

1. Stitch down the edge toward the corner and stop one seam-allowance's distance short of it: a quarter inch if you are sewing a quarter-inch seam, more if your seam is wider. Backstitch a couple of stitches and lift the foot.
2. Fold the binding straight up, away from the work, so its edge runs in line with the next side and a 45-degree crease forms at the corner.
3. Fold it straight back down, this time level with the next edge, keeping the diagonal tucked underneath. The top fold should sit flush with the edge you came from.
4. Start stitching again from the very top of the new side, and carry on to the next corner.

The stop point is what squares the fold. Stitch too far, into the seam-allowance zone, and the diagonal cannot pivot to a true right angle. The stop distance has to track whatever seam allowance you are sewing, which is why a quarter inch is a default and not a rule, since a wider seam stops wider. The other corner to watch is the fold itself: pulled too tight, with no slack in the diagonal, the finished corner cups instead of lying flat. Neither mistake outranks the other, and both stop happening once you have folded a few.

Easing Binding Around a Curve

A curve is where bias earns its name, and where the handling turns counterintuitive. The instinct is to keep the binding under even tension all the way round; the technique is to vary that tension by the direction the curve turns. Sew slowly, shape the binding a section at a time, and pin or clip generously so it holds the line you set.

On an inward, concave curve such as a neckline or an armhole, give the binding a gentle stretch as you pin, so it lies flat against the shorter inner edge and does not gape when it is turned. On an outward, convex curve such as a scallop or a rounded hem, do the opposite and ease a little fullness in, so the binding does not cup off the edge. The seam allowance underneath needs help too: clip into a concave allowance so it can spread open around the curve, and notch small wedges out of a convex one so the surplus has somewhere to go. The single rule under all of it is never to over-stretch. Bias pulled taut while you sew springs back the moment it leaves the machine, and a binding sewn tight will pucker the very edge it was meant to smooth. A steam press at the end settles any small unevenness that remains.

Joining the Two Ends

However you start the binding, the two ends have to meet somewhere, and a clean closing join is what separates a tidy finish from a lumpy one. There are two ways to close the loop, and they trade ease against bulk.

The diagonal-seam method gives the flattest result. Leave a gap as you attach the binding, stopping about six inches from where you began so roughly a twelve-inch span stays open, then bring the two tails together to seam them properly.

1. Lay the two tails along the edge so they overlap in the gap, and trim them to a tidy overlap.
2. Open the tails out, set them right sides together at a right angle, and stitch across the diagonal, corner to corner.
3. Trim the new seam to a quarter inch and press it open, then fold the binding back down and finish stitching it to the edge.

Because the seam runs on the diagonal, its bulk is spread along the binding rather than stacked in one spot, so the join ends up the same thickness as the rest and disappears once it is sewn down. The second method, the pocket or overlap close, folds one tail into a diagonal pocket and tucks the other inside it, with no cross-seam to stitch. It needs no measuring and looks like a seam, which is its appeal, but it is a little bulkier at the join because one binding nests inside the other, so reach for it when you want speed and the slight extra thickness will not show. The same diagonal logic joins individual strips end to end as you build the tape: ends at a right angle, a diagonal seam, pressed open. For the metric-minded, about six inches is roughly fifteen centimetres, and the yards to metres converter handles any figure you would rather read in centimetres. A scrappy, multi-fabric edge follows the same joins, and the scrappy binding planner counts the segments and the length the joins consume.

Common Bias Binding Mistakes

Most binding failures are not cutting errors, which the calculator heads off, but handling ones made in the last few minutes at the machine. A short checklist catches the usual suspects before they set.

• Sewing the bias taut. Stretched binding relaxes after stitching and ripples the edge. Let it feed through under its own weight; guide it, do not pull it.
• Tape too narrow to catch. A fold that barely reaches the back edge will skip in places when you topstitch. Cut a touch wider if a test length comes up short.
• Skipping the press. A strip that has not been pressed into firm folds will not wrap cleanly, and no amount of pinning fixes it at the machine. Press first, sew second.
• Forcing the corner. A mitre folded into a tight right angle with no slack will not lie flat. Leave the diagonal a little room to sit.

None of these is hard to undo if you catch it on a test piece, which is the real lesson: bind six inches of scrap in your chosen tape before you commit to the whole edge.

Bias Binding Glossary

A few terms recur through any binding tutorial, so here is what each one means in practice.

Mitre

The diagonal fold that turns binding around an outward corner. Folding the binding up to a 45-degree crease and back down squares the corner so it lies flat on both the front and the back instead of bunching at the turn.

Stitch in the ditch

Machine stitching that runs directly in an existing seam line, where it sinks out of sight. Securing the back of a binding from the front by stitching in the ditch catches the folded edge underneath while leaving almost no visible thread on top.

Easing

Working a slightly longer length of binding into a slightly shorter edge, or the reverse, without gathers or puckers. Bias eases well because it gives, and that give is how the binding rounds a convex curve without cupping.

Turn of the cloth

The small amount of width a binding loses as it wraps around the thickness of an edge. It is why a finished binding measures a shade narrower than the flat arithmetic predicts, and why a test length is worth pressing before you cut the whole strip.