When setting up a daybed, you can use a 36" wide antique bed (though we also have a 30" bed available.) This size was standard to single beds at the turn of the last century. The sizes then increased in increments of 6" to a 42' bed, called a large single, 48" called a 3/4 bed and finally 54" which is known as a full or double bed. About 50 years ago, queen and king size beds started to become popular. I've included a picture of one of our 36" pewter singles (S371 on page 2 of our Single beds catalog) to show what it could look like as a daybed. The trick is to make sure the headboard height and footboard height are approximately the same. Otherwise you end up with a single bed trying to masquerade as a daybed!