Base the decision on the finished dimensions, printer limits, trimming plan, and final binding edge. Letter size suits many reports and handouts, half-letter works for compact guides, legal supports longer forms, ledger accommodates wide layouts, and A4 fits metric workflows. If sheets will be trimmed after printing, allow room for crop marks and safe margins. Wide-format documents also need enough space along the intended binding edge for later punching. Confirm that covers, tabs, inserts, envelopes, and storage systems use compatible dimensions. A test assembly should include every component that affects the final size. Choosing a familiar paper format is not enough when the document will be folded, cut, or bound in an orientation that changes how the sheet is handled.