Binding is a strip of fabric that has to be longer than you think
Binding is the folded strip that wraps the raw edge of a finished quilt, covering the exposed batting and taking every bit of the abrasion the quilt will ever suffer. It is the last thing you make and the first thing that wears out, which is why its width, its grain and its join all matter more than their small size suggests.
The length starts as the perimeter — twice the width plus twice the length — but the perimeter is not enough. Each mitred corner folds a small amount of length into the mitre, and the two ends of the binding have to overlap and join to close the loop, which most quilters do with a diagonal seam needing several inches of tail at each end. Ten to twelve inches beyond the perimeter is the standard allowance and this calculator uses twelve by default.
Then there is the join between strips. Straight-grain binding is cut across the fabric, so each strip is only as long as the usable bolt width — about 41 inches after the selvedges come off a 42-inch cotton. Those strips are joined with a diagonal seam so the bulk is spread over an inch or two rather than stacked in one place, and that diagonal seam eats roughly one strip width of length per join. On a queen-size quilt with eleven strips, that is ten joins and about 25 inches of binding you never see. Estimates that multiply the perimeter by nothing and divide by 41 are the ones that run out on the fourth side.
Where the cut width comes from
Double-fold binding, sometimes called French binding, is a strip folded in half lengthwise so the edge that shows is a fold rather than a raw edge. Work out where the fabric goes and the cut width follows. Half the strip lies on the front, of which the finished width shows and an equal amount is taken by the seam allowance; the fold wraps the thickness of the quilt sandwich; and the other half lands on the back, where it again needs the finished width plus its turn-under. That gives a cut width of four times the finished width, plus twice the edge thickness, plus a quarter inch for what quilters call turn of cloth — the fabric consumed by the folds themselves.
Run that with the numbers everyone uses and it lands where practice has landed. A quarter-inch finished binding on a low-loft cotton batting wants a 1.5-inch strip; a half-inch finished binding on the same batting wants 2.5 inches, which is exactly the strip width sold pre-cut everywhere. Go up to a high-loft polyester batting and the same 2.5-inch strip finishes narrower, because more of the fabric is spent crossing the thicker edge.
This is why the calculator shows two width figures. One is the cut width the geometry calls for given the finish you asked for; the other is the finish your chosen cut width will actually produce on your edge thickness. Neither is wrong. Most quilters pick a strip width they like and accept the finish it gives, and knowing the number in advance is what stops you from being surprised.
Single-fold binding, with a raw edge turned under rather than a fold, uses roughly half the width — twice the finished width plus two seam allowances. It is less durable because only one layer of fabric takes the wear, so reserve it for wall hangings and items that will not be washed.
Worked example: a 60 × 80 inch quilt in 2½-inch strips
The quilt trims to 60 by 80 inches. You are binding with straight-grain 2.5-inch strips from a 42-inch cotton, trimming half an inch of selvedge from each side, and allowing 12 inches for corners and the closing join.
- Perimeter. 2 × (60 + 80) = 280 in.
- Binding length. 280 + 12 = 292 in.
- Usable strip length. 42 − (2 × 0.5) = 41 in.
- Strips. Seven strips give (7 × 41) − (6 × 2.5) = 287 − 15 = 272 in, which is short. Eight give (8 × 41) − (7 × 2.5) = 328 − 17.5 = 310.5 in, which covers it. So 8 strips.
- Fabric. 8 × 2.5 = 20 inches of fabric depth, which is 20 ÷ 36 = 0.56 yd. Buy 5/8 of a yard.
- Cut width check. For a 3/8-inch finish on a 1/8-inch edge, the geometry wants (4 × 0.375) + (2 × 0.125) + 0.25 = 2.0 in. Your 2.5-inch strip instead finishes at (2.5 − 0.25 − 0.25) ÷ 4 = 0.5 in.
- Bias alternative. A continuous bias would need a square of side √(292 × 2.5 × 1.05) = 27.7, rounded up to 28 inches — 0.78 yd, about 40% more fabric than the straight-grain route.
Note how much the joins cost. Ignore them and 292 ÷ 41 = 7.1 suggests eight strips too — but only just, and on a queen quilt the same shortcut suggests ten strips where eleven are needed. The margin disappears exactly when the quilt gets big enough for the error to hurt.
Straight grain or bias, and how to read the yardage
Straight-grain binding is cut across the width of the fabric, on the crosswise grain. It has almost no stretch along its length, which makes it stable and easy to apply to straight edges, and it is the most economical route because every inch of a strip becomes binding. Use it for any quilt with straight sides and mitred corners, which is nearly all of them.
Bias binding is cut at 45 degrees to the grain, which gives it stretch along its length. That stretch is what lets it travel round a curve or a scallop without rippling, and it also makes the binding wear better on a quilt that gets heavy use: on straight grain a single thread runs the length of the fold and abrades all at once, while on bias the threads cross the fold and wear is distributed. It costs more fabric, because a square has to be big enough in both directions to yield the length you need.
The continuous bias method is the efficient way to cut it. You take a square, cut it corner to corner, join the two triangles into a parallelogram, then mark strip lines and sew the piece into a tube offset by one strip so a single continuous strip spirals off it. Because the whole square is consumed, the side you need is close to the square root of the binding length times the strip width, with a small allowance for the corner triangles.
Whichever route you take, round the yardage up at the counter. A binding is the one component you cannot make from an offcut if you run out, because a colour or print break in a binding is visible around the entire quilt. Buying a quarter yard more than the calculation costs a couple of dollars and removes that risk entirely. Where the binding comes off the same fabric as the back, plan both at once with the quilt backing yardage calculator.
Cut width for common finished bindings
| Finished binding width | Cut width on 1/8 in edge | Cut width on 1/4 in edge | Cut width on 1/2 in edge |
|---|---|---|---|
| 1/4 in (0.250) | 1½ in | 1¾ in | 2¼ in |
| 3/8 in (0.375) | 2 in | 2¼ in | 2¾ in |
| 1/2 in (0.500) | 2½ in | 2¾ in | 3¼ in |
| 5/8 in (0.625) | 3 in | 3¼ in | 3¾ in |
| 3/4 in (0.750) | 3½ in | 3¾ in | 4¼ in |
Read down the column for your batting: a low-loft cotton quilt sits near 1/8 in at the edge, a wool or high-loft polyester nearer 1/4 in, and a heavily stuffed comforter more. The ubiquitous 2½ in strip is the half-inch row on low-loft batting.
Mistakes that leave you short or lumpy
- Dividing the perimeter by the fabric width. Every diagonal join eats about a strip width of length. On ten joins that is over two feet of binding you never get.
- Forgetting the corner and closing allowance. Mitres consume length and the two ends have to overlap. Ten to twelve inches beyond the perimeter is the standard.
- Joining strips with a straight seam. A straight join stacks four layers of fabric in one place and shows as a lump under the stitching. Join on the diagonal so the bulk spreads over an inch or more.
- Leaving selvedges in a binding strip. Selvedge shrinks differently and will pucker the binding at the first wash.
- Using straight grain on a curved edge. It cannot follow the curve without rippling on an outside curve or pleating on an inside one. Curves need bias, without exception.
- Measuring the quilt top rather than the trimmed sandwich. Bind to the trimmed size, and measure through the middle rather than at the edges.
- Cutting the strip width by rule of thumb without checking the batting. The same 2½ in strip finishes noticeably narrower on a high-loft batting because more fabric is spent crossing the edge.
- Piecing the binding from two different cuts of the same fabric. Any colour break shows all the way round the quilt. Cut all the strips from one piece.
Other edge finishes and where this calculation stops
Binding is not the only way to finish a quilt edge. A knife-edge or self-binding finish turns the backing over to the front and stitches it down, which costs no extra fabric but gives only one layer at the wear point. A facing turns the binding entirely to the back so no frame of colour shows on the front, which suits art quilts. Piping inserted under the binding adds a fine line of contrast and needs its own bias strip plus cord. None of these are calculated here; this page covers the standard applied double-fold binding.
If your quilt has scalloped or curved edges, calculate the length from the actual edge rather than the perimeter of the bounding rectangle — a scalloped edge can be 15% longer than the rectangle it fits in — and always cut bias. Measure the curve with a flexible tape or a length of string laid along it, then enter that total as the perimeter by putting half of it into each of the two dimension fields.
Binding is usually the last thing you cut from a quilt fabric purchase, so it is worth planning into the same cut as everything else. Two thirds of a yard binds a queen quilt; you may well already have that in the offcut left from the backing. The fabric yardage calculator shows how strips and pieces nest together on the same length of fabric, and if you are still cutting the top, the half square triangle calculator gives the cut sizes that determine the finished dimensions you are binding to.