CLEAR INPUTS. EXPLAINED RESULTS.

Quilt backing &
binding formulas.

These calculators make their assumptions visible, so you can decide whether a plan fits your project.

Backing: account for every seam

Use the quilt backing calculator to compare the two panel layouts using your own measurements.

First, add twice the chosen overage to the quilt width and length. A run of n panels of usable width F, sewn with allowance s on each joined edge, covers:

Sewn coverage = n × F − 2 × s × (n − 1)

We choose the smallest whole number of panels that covers the required dimension. Panels are cut across the full usable width of the fabric. Total fabric length is panel count times cut length. We compare the two seam directions unless you lock one, and round the purchase up only after converting to yards or meters.

For example, two 42-inch panels with 1/2-inch allowances make 83 inches of sewn width, not 84. A backing even slightly wider than 83 inches needs another panel in that orientation.

Binding: enough length after the joins

Use the quilt binding calculator to turn the required length into a strip count and fabric purchase.

For a rectangular quilt, the required length is the perimeter plus your finishing allowance. For n strips of usable length F, with length loss j at each join:

Joined length = n × F − j × (n − 1)

For 45-degree diagonal joins of straight-grain strips, j is one cut strip width. For straight joins, it is twice your selected seam allowance. We choose the smallest strip count with enough joined length. Fabric taken from the bolt is strip count times cut strip width.

The finishing allowance covers corners and closing the binding loop; it is not another allowance for joining the individual strips. The main calculator uses straight-grain strips. A separate bias-strip planner is available below its results.

Advanced three-piece backing

For an assembly width W, height H, usable fabric width F and seam allowance s per edge, cut one F × H panel. The side column needs width C = W − F + 2s. Cut two pieces each (H + 2s) ÷ 2 across the bolt and C down the bolt, then rotate them. This is only offered when their across-bolt dimension fits F. Join the two side pieces, then join the column to the main panel. Coverage is exactly W × H and cut length is H + 2C. Both assembly orientations are checked. Locked fabric direction disables this method.

The plan has two seams and a T-junction. It is unsuitable for directional prints, nap or a quilter who does not accept the layout. It is an optional alternative, not part of the main full-panel shopping list and not a search over all possible cutting arrangements.

Separate bias-strip geometry

The bias planner cuts individual rectangular strips at 45° inside one or more squares. In coordinates rotated 45°, a square of side S satisfies |u| + |v| ≤ S ÷ √2. For each band of the requested strip width, the shorter available length at its two edges defines the squared-end rectangle. Lengths round down to 0.01 in, end triangles are discarded, and strips no longer than two strip widths are omitted.

Total usable length is the sum of strip lengths minus one strip width for every diagonal join. The planner searches square sides in ½ in steps that fit the usable bolt width. Squares are placed consecutively down the bolt, not nested. It chooses the smallest rounded purchase among those candidates, then prefers fewer strips. This is not continuous tube binding, does not optimize every possible layout, and does not allow for shrinkage or fabric preparation.

For curved projects enter the actual measured edge length. The rectangle perimeter is only a starting value. See the illustrated project example for full-panel preparation and a geometrically checked three-piece comparison.

Reference size examples

These are planning examples, not standard finished quilt sizes. Every row assumes 42-inch usable fabric, 4 inches of backing extra on each side, 1/2-inch backing seam allowances, 2 1/2-inch straight-grain binding strips, diagonal joins, 12 inches of finishing allowance, and purchases rounded up to the next 1/8 yard.

Actual bed and quilt dimensions vary. Enter the measured quilt top in the calculators before buying or cutting fabric.

Units and rounding

One inch is 2.54 centimeters; one yard is 36 inches. Measurements remain at full calculation precision when you switch display units. Purchase units are chosen separately. Buying in increments of 1/8 yard is different from buying in increments of 0.1 meter, so rounded purchases can differ.

Scope and limitations

These are planning estimates. They exclude fabric defects, shrinkage, repeat matching and arbitrary offcut layouts. Confirm your longarm service’s overage and seam-placement requirements, use actual usable fabric measurements, and check the plan before cutting. Arithmetic tests do not replace practical sewing validation.

About this toolkit and its checks

Patch & Measure is the independently maintained quilt calculator toolkit published at quiltmathkit.com. Its formulas are shown on this page, and automated tests cover seam boundaries, strip joins, unit conversion, purchase rounding and the worked examples above. The browser-based tools are also checked across desktop and mobile layouts before release.

These checks establish the software’s arithmetic behavior; they are not a claim of professional quilting certification or independent field validation. If you use a longarm service or a technique with different allowances, follow that service’s requirements. Questions and reproducible corrections are welcome at support@quiltmathkit.com. Last reviewed September 23, 2026.