Measure the strips before sewing
This calculator is for sets made from strips of equal cut width. Enter the number of strips in one set and the length of the shortest strip. That shortest length limits the usable length of the whole set. Enter any trimming at each end separately, rather than subtracting it from the strip length first.
Seams reduce the assembled width
Three 2½-inch strips sewn together with ¼-inch seams make a strip set 6½ inches wide before its outer edges are sewn into another unit. There are two joins, and each takes up two seam allowances. The result shows this unfinished set width alongside the length available for crosscutting.
Work out how many sets to make
Starting with 40-inch strips and trimming ½ inch from each end leaves 39 inches. You can cut fifteen 2½-inch units from that length. If you need 24 units, sew two sets: they'll produce 30 units, leaving six extra. The source-strip count tells you how many long strips to prepare for those sets.
Keep an eye on the print direction
Crosscut units keep the fabric orientation of the sewn strip set. Check directional prints before sewing a batch, especially if the units will be turned in the block layout. The source-strip row and crosscut-unit row describe the same fabric at different stages; don't add their material amounts together.