If you have an antique bed, and I’m not talking about something grandma bought at Sears, but an old bed that was built back when hand craftsmanship reigned supreme, there is a chance that it may need a customized mattress size.

Long ago there was a size called Three Quarter Bed (3/4 mattress). It was wider than a twin, but not quite as wide as a full. I did not run into this often. But if someone mentioned antique or anything else along those lines, just to be safe, I would ask them to confirm the size.