MEASURE TWICE, CUT ONCE

The math behind your quilt.

A useful estimate should tell you what it assumes. Here is exactly what our rectangular patchwork planner calculates.

Finished sizes and seam allowances

All calculations use inches internally. One inch is exactly 2.54 cm; one yard is 36 inches or 0.9144 m. Display rounding does not change the stored geometry. Enter finished block dimensions, excluding seam allowance. A cut block is finished width + twice the seam allowance by finished height + twice the seam allowance.

For example, a finished 6 × 6 inch block with ¼-inch seams needs a 6½ × 6½ inch cut square. Six columns and eight rows make a 36 × 48 inch center. A 3-inch finished border on each side makes the final quilt 42 × 54 inches.

Blocks and fabric strips

The diagonal palette repeats fabric A, B, C using (row + column) modulo 3. We count each fabric’s blocks individually. Pieces per crossgrain strip = floor(usable fabric width ÷ cut block width). Required strips = ceiling(piece count ÷ pieces per strip). Raw fabric length = strip count × cut block height.

With 42-inch usable fabric and 6½-inch squares, each strip yields six blocks. The default quilt uses 16 blocks per fabric, requiring three 6½-inch strips, or 19½ inches of fabric length per color.

One straight, pieced border

The planner attaches side borders first, then top and bottom. The strip width is finished border width + twice the seam allowance. Side border cut length is center height + twice the seam allowance. Top and bottom cut length is finished quilt width + twice the seam allowance.

For a target border length L, fabric width W, and seam s, full-width strips per border = max(1, ceiling((L − 2s) ÷ (W − 2s))). Join them with straight seams, then trim. Each of the four borders receives its own strips. Leftover pieces are not reused. This is conservative and easy to follow, not optimal. Border yardage stays separate from the similarly colored blocks.

Backing: vertical panels

Backing target dimensions are finished quilt dimensions + twice the extra per edge. Panel count = max(1, ceiling((backing width − 2s) ÷ (usable fabric width − 2s))). Each full-width panel is cut to backing height. Raw fabric length = panels × backing height. Join long edges with the selected seam allowance; trim the assembled backing to its target.

The default quilt needs a 50 × 62 inch backing. Two 42 × 62 inch panels give 83½ inches of joined width before trimming, using 124 inches of fabric length. This deliberately uses vertical panels; rotating or reusing offcuts could reduce yardage. Confirm overhang and backing seam requirements with your longarm quilter.

Straight-grain, double-fold binding

Required binding length = 2 × (quilt width + quilt height) + 12 inches. The extra covers corners and the final joining operation. Diagonal strip joins consume approximately one binding strip width per join. Strip count = max(1, ceiling((required length − strip width) ÷ (usable width − strip width))). Raw yardage comes from strip count × strip width. This is not bias binding and does not model curved edges.

The default perimeter is 192 inches, so the target is 204 inches. Six 42 × 2½ inch strips provide 239½ inches after five diagonal joins.

Buying allowance and rounding

Each shopping-list line is independent. Multiply its raw fabric length by (1 + safety percentage ÷ 100), divide by 36, and round upward to the next ⅛ yard. A zero quantity stays zero. The default 10% allowance produces ⅝ yard for each block fabric, ½ yard each for the side and top/bottom borders, 3⅞ yards of backing, and ½ yard of binding: 7¼ yards total.

Metric purchase values convert the rounded yard quantities; they are not rounded to a store’s metric selling increment. Ask your retailer to round up if necessary. Display dimensions are rounded to three decimals. Construction instructions retain exact inch values.

What this planner does not estimate

No batting, shrinkage allowance beyond your chosen safety margin, directional matching, fussy cutting, complex pieced blocks, sashing, multiple borders, or mitered corners. Fabric width must exclude selvages. A suggested cutting plan is not proof of optimal fabric use. Always verify your measurements and sew a test block before cutting the full project.