Selvedge & Sage

How we calculate

The mathematical engine is independent of the page interface. It uses fixed geometry and arithmetic, with no AI-generated numbers or external calculation service.

What has been checked

The test suite checks hand-worked examples, seam and fabric-width boundaries, small through oversized quilts, centimetre conversions, strip capacity and diagonal rectangle coverage. Tests use separate quadratic and geometric checks for the diagonal method. The source includes the test cases and full mathematical notes.

What still needs a quilter

The practical cutting and joining instructions have not yet had an experienced-quilter review. We do not claim professional validation. Fabric behaviour, stretching, squaring, shrinkage and a quilting service’s requirements need real-world judgement.

Units and rounding

Internal calculations use inches; 1 inch is exactly 2.54 centimetres. Changing units preserves the same measurements. Purchases round up to the next ⅛ yard or 0.1 metre. These are this website’s policies, not a claim about every retailer. Cut dimensions display up to three decimals, rounded up where necessary. Measure and trim actual fabric to the specified dimensions.

Quilt backing calculator

Required backing = quilt size + twice the overhang. For a joined width B, usable bolt width F and seam allowance s, the smallest panel count is ceil((B − 2s) / (F − 2s)). Every join consumes 2s. Yardage is the sum of panel cut lengths, plus any separate matching reserve.

Panels are balanced in width, all cut from one fabric, with ordinary straight seams pressed open. The least fabric result is selected among the two supported regular-panel layouts. Scraps, inset strips and diagonal piecing are outside this comparison. Fabric width means usable width after selvedges; shrinkage and squaring-up fabric are not automatically included.

Quilter’s Paradise: backing methods

Quilt binding calculator

Working length = 2 × (width + length) + extra. If join loss is j and fabric width is F, n strips give nF − (n − 1)j. Select the smallest whole n that reaches the working length. For a 45° strip join j is the cut strip width; for a straight join j = 2 × seam allowance. Fabric length = n × cut strip width.

This is a straight-grain, double-fold strip plan for a rectangular quilt. It does not calculate continuous bias binding or curved edges. Extra length covers corners and the final closing join; it is additional to the loss at strip-to-strip joins. Batting thickness and attachment technique affect the visible binding width, so test a short sample.

APQS: binding strip cutting chart · Quilting guild: borders and bindings

Quilt border calculator

Cut width = finished border width + 2s. Straight side lengths = centre length + 2s; top and bottom lengths = centre width + twice the border width + 2s. Mitred cut lengths = the centre dimension + twice the cut border width + 2s + two extra tails. Each border increases finished width and length by twice its finished width.

One fabric per border; consistent seam allowances; no corner blocks, sashing, pattern repeats or fussy cutting. Widthwise strips use straight end joins, not diagonal strip joins. Every side has its own balanced pieces; this conservative plan does not reuse offcuts. Long strips are packed in lanes across the bolt. Mitred piecing is excluded when a join would land in a corner tail.

American Patchwork & Quilting: border dimensions · American Patchwork & Quilting: mitred borders

Quilt fabric calculator

Columns = ceil(target width / finished block size); rows = ceil(target length / finished block size). A block has 1, 4 or 9 squares. Cut square size = finished block size / squares along one side + 2s. Squares per strip = floor(usable fabric width / cut square size). For each fabric, strips = ceil(piece count / squares per strip).

Exact piece counts apply to the displayed square-based layout only. Yardage is an estimate for strip cutting, with a separate percentage reserve. There is no sashing, border, appliqué, half-square triangle, on-point setting or stripe matching. Fabric A/B are pooled yardage, not estimates for individual prints in a scrappy quilt.

Quilter’s Paradise: piece-count yardage calculator

Diagonal quilt backing calculator

For target backing B × H and usable fabric width F, ideal seam-free fabric length is L = HF / (2F − B), the same as Flynn’s published equation. With a seam allowance s on each diagonal edge, solve HF = L(2F − B) − 2s√(L² + F²). The extra term accounts for the seam measured perpendicular to the sloping edge.

A single non-directional fabric; no pattern matching. Supported when backing width + 2s is no more than 1½ usable fabric widths. If one width already fits, there is no need for a diagonal seam. The calculation models flat, unstretched fabric. A longarm service must accept a diagonal seam before you choose this method.

John Flynn: original method and formula · Jinny Beyer: diagonal backing worksheet