If your table is 48" wide, and your runner is 18" wide that will leave 15" on each side for place settings, which sounds good to me. You need enough room so your stemware isn't on the runner and may tip. I like runners to run over the edge of the table, so the length is good too. My main dining room table is 17' long so my runner (only have a Christmas one) is over 6 yards long.