Calculation Methodology

Core principles

• Exact vs. purchase. We always show the precise mathematical requirement and a separate, conservative amount to buy. Material requirements are never rounded down.
• One base unit. All lengths convert to millimeters internally using exact constants (1 in = 25.4 mm, 1 yd = 914.4 mm), so results are identical whether you work in inches or centimeters.
• Stated assumptions. Each result lists the defaults it used, and important ones — fabric width, overhang, seam allowance — are yours to override.

Quilt backing

Backing width and length add your overhang to both sides of the quilt. The back is pieced from full-width panels; we test seams running each direction and keep the cheaper one (directional prints skip rotation). Each panel’s cut length includes a seam allowance per join. Total length becomes yards, rounded up to the next ¼ yard.

Quilt binding

Perimeter = 2 × (width + length), plus a corner/join/overlap allowance. Strips are cut across the fabric width; strip count = binding length ÷ fabric width, rounded up. Fabric length = strips × strip width, converted to yards and rounded up to the next ⅛ yard.

Quilt size

Finished size = (blocks × block size) + sashing between blocks + borders on both sides. Sashing is counted between blocks only. We match the result to the closest standard US size.

Fabric yardage

Pieces per row = fabric width ÷ piece width (rounded down); rows = quantity ÷ pieces per row (rounded up); fabric length = rows × piece length. Seam allowance is added to every edge, and we keep the cheaper of the as-entered and rotated layouts. Rounded up to the next ¼ yard.

Curtain fabric

Gathered width = window width × fullness. Fabric widths = gathered width ÷ fabric width (rounded up, at least one per panel). Cut length = drop + header + hem, rounded up to a whole pattern repeat when specified. Total = widths × cut length, rounded up to the next ¼ yard.

Unit conversion

Values pass through the millimeter base unit with exact constants, making conversions reversible. Imperial results also show a fraction rounded to the nearest eighth.

A note on estimates

These tools produce planning estimates. Fabric shrinks, prints skew, and cutting isn’t perfect — when a project is precious, buy a little extra and confirm against your own pattern or quilter’s requirements before cutting.