Binding a Quilt: Strips, Bias and the Fabric to Buy

Straight grain or bias, and when the choice is not free

Strips cut across the width of the fabric follow the straight grain: they are stable, they use fabric efficiently and they are what the calculator assumes. Strips cut at forty-five degrees are bias: they stretch, which is the point, because only a stretchy strip will go round a curve without puckering. A quilt with square corners does not need bias, and a quilt with a scalloped or rounded edge cannot be bound without it.

The cost of bias is fabric. Cutting on the diagonal wastes the two triangular corners of whatever piece you cut from, and the usual working figure is that bias binding needs about a third more fabric than straight-grain for the same finished length. There is a second reason to choose it even on a square quilt: a straight-grain strip binds a straight edge along a single line of threads, and if that quilt is used and washed for years, one line of threads is what eventually goes. Bias spreads the wear across the weave.

The strip width is the number that moves the fabric

Perimeter sets the strip count, and strip count is coarse — it changes only when you cross a multiple of the bolt width. Strip width, by contrast, multiplies the whole result: the same seven strips at 5.7 cm take 40 cm of fabric, at 6.5 cm take 46 cm, at 8.9 cm take 62 cm. Going from a narrow finish to a wide one costs half as much fabric again on exactly the same quilt.

The width you choose also has to match the loft of the quilt. A double-fold binding wraps the raw edge twice, so the finished width on the front is roughly a quarter of the cut strip minus what the batting thickness eats. A thin cotton batt and a 6.35 cm strip give a tidy narrow finish; the same strip on a thick polyester batt is tight and pulls, and the corners will not sit. Where a quilt is lofty, go up a width rather than fight it.

Corners are where a binding is judged

A mitred corner is made by stopping the seam a seam-allowance short of the edge, folding the strip up at forty-five degrees, then folding it back down along the next side. The fold consumes a small amount of strip at each corner — a centimetre or so on a standard binding, four corners, so four centimetres — which the twenty-five centimetre join allowance already covers. What it does not cover is a corner sewn without the stop: run the seam to the edge and the strip has nowhere to pivot, so the corner either bulges or pulls the quilt out of square.

The other corner failure is arithmetic rather than technique. If the quilt is not actually square — and after quilting it very often is not — a binding cut to the measured perimeter will run out on the long side or bag on the short one. Measure both widths and both lengths, use the larger of each pair, and ease the surplus in along the sides rather than at the corners, where it shows.

Frequently asked questions

How much binding fabric for a double quilt?

For 150 × 200 cm with 6.5 cm strips: seven strips and 46 cm of fabric off a 110 cm bolt, six strips and 39 cm off a 140 cm bolt. Round up to the nearest quarter metre when buying, because the strips have to be cut square to the selvedge and the first straightening cut takes a couple of centimetres.

Why 25 cm of overlap and not 10?

Because the two ends are joined on the diagonal, and a diagonal join across a 6.5 cm strip consumes about 9 cm of length on its own before anything is trimmed. Ten centimetres leaves you closing the loop with no slack, on a quilt that is by then bulky and awkward to handle. Twenty-five gives room to make that last seam comfortably and to trim it square afterwards.

Can I use ready-made bias tape?

You can, and for a small project it is a reasonable saving of effort. For a bed quilt it is usually a false economy: commercial bias tape is cut narrow, in a lighter-weight cotton than a quilt top, and it wears through at the edge years before the quilt does. It also comes in a fixed palette, which on a scrappy quilt is the visible compromise. Cut your own from the same fabric range and the binding ages with the quilt instead of ahead of it.