Use the center measurement the model expects
Enter finished center dimensions between intended outer seam lines. The raw center includes an outside allowance. Measure and square the actual work before cutting.
The sides-first construction
For center W × H, border B and seam S: strip width = B + 2S; side length = H + 2S; top/bottom length = W + 2B + 2S.
A 50 × 60 center, 3-inch border and ¼-inch seams need 3½-inch strips: two at 60½ inches, two at 56½. Finished size: 56 × 66.
Long pieces may need joining
Each straight join consumes 2S. Two 42-inch strips with ¼-inch seams yield 83½ inches. Each example border needs two strips: eight total, using 28 fabric inches, rounded to 1 yard.
Offcuts are not reused between borders. No mitered corners or cornerstones are modeled.
Carry the new dimensions into the next step
Calculate extra borders in sewing order. Take final dimensions to binding, backing and batting. Use the block calculator for the center.