Start with cut dimensions
Finished dimensions need seam allowance on both opposite edges; cut dimensions already include it. Keep quantity, direction, and any WOF-strip requirement with each piece.
Use usable width
Count how many pieces fit across fabric after selvages, then round rows upward. Apply purchase safety after the layout and round the purchase upward to the shop increment.
Combine a real project
The fabric yardage calculator handles one repeated rectangle. For multiple sizes and stock on hand, use the project fabric planner.