Binding length is your quilt's perimeter, plus extra for the four corner mitres and the diagonal seam that joins strips end to end — not just the perimeter alone, which is the most common way these numbers come out short. For a queen quilt (90 × 108 in) with double-fold ⅜" binding and this calculator's default assumptions, that works out to about 408" of binding and ⅝ yard of fabric, cut into 11 strips. The calculator above runs the same arithmetic for any size, with every assumption editable and shown, not buried in a black box.
Why the Answer Isn't Just Perimeter Divided by Width
Take the raw perimeter of a quilt and divide by your fabric's usable width, and you'll come up short at the very end of sewing the binding on — the point where it's hardest to fix. Two things eat into the number that a plain perimeter calculation ignores. First, each of the four corners needs a little extra fabric to fold a clean 45° mitre rather than a bunched, overlapping corner. Second, one strip is almost never long enough to go all the way around a quilt, so strips get joined end to end with a diagonal seam — and that seam consumes a small amount of fabric at every join.
The convention in circulation — Missouri Star Quilt Company's tutorials and generic quilting-guild references both land in the same range — is to add roughly 10" to 12" combined for mitres and the final join, on top of the raw perimeter. This calculator defaults to 2" per corner (8" total) plus a flat 4" for joins, landing at 12" — the top of that range — and both figures are editable above the results.
Double-Fold vs Single-Fold Binding
Double-fold binding — also called French binding — is cut as a single strip, then folded in half lengthwise before it's sewn on. That fold means two layers of fabric wrap the quilt's edge, which is the part of a quilt that takes the most handling, washing, and wear over its life. Single-fold binding skips that fold: the strip is sewn on as a single layer, with its raw edges turned under instead of doubled.
Single-fold uses noticeably less fabric — the cut strip only needs to be about half as wide — but a single layer wears through faster at exactly the point where a quilt gets folded, dragged across furniture, and washed hundreds of times. That's the whole reason double-fold dominates quilt patterns and is this calculator's default: it puts two layers of fabric exactly where the abrasion happens.
Straight-Grain vs Continuous Bias: Why Curves Need the Diagonal
Straight-grain binding is cut with the strip's length running parallel to the fabric's selvage (or, less commonly, crosswise to it). Along a straight edge with only 90° corners, that grain direction gives the binding the least stretch and the most strength — exactly what a straight edge needs, and it uses less fabric than cutting on the bias for the same length.
Continuous bias binding is cut at 45° to the grain instead. Fabric cut on the true bias has a small amount of give, which lets a strip curve smoothly around a scalloped edge or a rounded corner without the puckers or small pleats a straight-grain strip would need to fake the same curve. The trade-off is real: bias strips use more fabric for the same finished length (the diagram and the math below show why), and they're more work to cut. Reach for bias only when the quilt's edge genuinely curves — a straight-edged quilt gains nothing from it.
How This Calculator Gets Your Cut Strip Width
The formula for double-fold binding used here is:
cut width = (finished width × 4) + (2 × seam allowance)
The ×4 comes from the strip being folded in half — two layers — and each layer showing the finished width on both the front and the back of the quilt. The seam allowance is consumed twice: once sewing the raw strip to the quilt top, and again in the fold that wraps the binding to the back. Single-fold binding, with only one layer instead of two, uses ×2 in place of ×4.
What isn't standardised is the seam allowance itself. Some sources use ¼" — the standard quilting piecing seam — which gives a ⅜" finished binding a 2" cut width. Others use a flat ½" for extra ease wrapping around a thicker batting, which gives the same ⅜" finished binding a 2.5" cut width — a number several published patterns also use. Neither is wrong; they're different choices for how much slack to leave. This calculator defaults to the ¼" convention and lets you switch to ½" and watch every downstream number — strip count, fabric length, yardage — update to match.
The Diagonal Seam: Why a Straight Join Is Wrong
When one strip isn't long enough to bind a whole quilt, strips get joined end to end before the binding is attached. Sewing that join straight across — the obvious way to do it — puts a hard lump of four seam-allowance layers directly at the point where the binding later folds over the quilt's edge. It shows on the front, catches under a hand, and is genuinely uncomfortable to press flat.
A diagonal seam, sewn at 45° across the overlapped strip ends, spreads that same thickness over a much longer stitch line, so it presses flat and the bulk is distributed rather than stacked in one spot. It costs a small amount of extra fabric at every join — trimmed seam allowance plus the length the diagonal itself consumes — which is part of the flat join allowance this calculator adds to the raw perimeter, alongside the four corner mitres.
The Continuous Bias Square: the Math Behind the Diagram
Continuous bias binding starts from a single square of fabric, cut once along one diagonal into two triangles, then re-joined offset by exactly one strip-width to form a parallelogram. Lines are marked across that parallelogram, spaced at the strip width, and it's folded into a tube and cut in one continuous spiral — which is what turns a square into one long bias strip with no seams inside it.
Cutting the square into two triangles and re-joining them offset doesn't create or destroy fabric — it rearranges the same area into a different shape (setting aside the sliver the offset seam itself consumes). So the parallelogram's area is, to a close approximation, the same as the original square's: side². Once that parallelogram is cut into one continuous strip of width w and length L, its area is also w × L. Setting the two equal —
side² ≈ w × L → side = √(w × L)
— gives the square's side length directly from the strip width and the total binding length you need. The units check out: inches × inches gives square inches, and the square root of square inches gives inches back. It's an approximation, not an exact figure — it ignores the small amount of fabric the two seams in the technique itself consume — so treat the result as a slight underestimate and round up when you buy. The diagram above draws the marked cutting lines at their true relative spacing across the square, using the same geometry: the number of parallel lines a strip width w apart fits across a square of side S works out to S√2 ⁄ w, which is exactly what's rendered, not a stand-in illustration.
Standard Quilt Sizes and Typical Binding Yardage
These are commonly used finished quilt dimensions — roughly a mattress size plus a drop — not a single universal standard; individual patterns vary, sometimes by several inches. Use Custom in the calculator above for your quilt's exact measurements. The yardage below assumes this calculator's defaults: double-fold ⅜" binding, ¼" seam allowance, 40" usable fabric width, and the 12" combined mitre-and-join allowance.
| Size | Dimensions | Binding fabric |
|---|---|---|
| Crib / Baby | 36 × 52 in | ⅜ yd |
| Throw | 50 × 65 in | ½ yd |
| Twin | 70 × 90 in | ½ yd |
| Full / Double | 85 × 95 in | ⅝ yd |
| Queen | 90 × 108 in | ⅝ yd |
| King | 108 × 108 in | ¾ yd |
Measuring Your Quilt Accurately
- Measure at the largest points. Edge to edge, not diagonally, and ideally before quilting has drawn the edges in slightly.
- Check both sides of each dimension. If the quilt isn't perfectly square, measure width at both the top and bottom, and height at both sides, then use the larger of each pair — binding has to reach the longest edge, not the shortest.
- Enter your measurements, or start from a preset. Treat a standard size as a starting point, not a guarantee — patterns vary.
- Pick straight-grain or continuous bias based on the quilt's edges, not habit: straight edges and 90° corners want straight-grain; any curve or scallop wants bias.
Buy a little more than the calculator says if you're new to binding, if your project includes multiple diagonal joins, or if the fabric is a directional print that limits how you can lay out strips. A partial extra strip is cheap insurance against running short two-thirds of the way around a finished quilt.