Give those feet a little more breathing room but still enjoy the roomier feel of a traditional king. A few inches make all the difference with a California king mattress, at 72 inches wide and 84 inches long. If you're on the taller end of the spectrum, extra legroom brings extra comfort—and at no extra cost. A lot of sleepers think that California king mattresses are actually larger than traditional kings, when really they have the same surface area.