Calculation Methodology
QuiltMath uses deterministic browser-local formulas. Results are conservative planning estimates, not a replacement for pattern instructions or a quilter's project requirements.
Backing dimensions
The selected overage is added to every side of the finished quilt top.
required length = quilt length + (2 × overage per side)
Panel coverage and seams
For each orientation, the calculator adds fabric-width panels until their joined coverage meets the target. Each seam consumes the entered allowance on both joined edges.
raw roll length = panels × panel cut length
Vertical and horizontal seam layouts are both tested. The recommendation uses the smaller rounded purchase length, then estimated layout offcut as a tie-breaker.
Purchase rounding
Fabric is always rounded upward, never to the nearest increment.
metric: next 0.1 meter
Binding formula
working length = perimeter + extra length
strip count = max(1, ceil((working length − cut strip width) ÷ (usable WOF − cut strip width)))
length after joins = strip count × usable WOF − (strip count − 1) × cut strip width
fabric depth = strip count × cut strip width
For square-overlap diagonal strip joins, each intermediate join consumes one cut strip width. The extra working length separately allows for corners and the final end join. Strip width must be smaller than usable WOF. Purchases round up to ⅛ yard or 0.1 meter; shrinkage and pattern matching are not included. The calculator covers straight-grain crosswise strips for double-fold binding, not continuous bias binding. See tested worked examples. Formula reviewed September 6, 2026.
Border formula
side cut length = quilt length + 2 × seam allowance
top/bottom cut length = quilt width + 2 × finished border width + 2 × seam allowance
The border calculator assumes straight rectangular borders attached to the sides first, then top and bottom. Mitered corners require different geometry.
Units and privacy
Metric values are converted to one internal inch model, calculated once, then converted for display. No calculation input is sent to a server by the v1 site.