The dimensions of a California king mattress is 72 inches by 84 inches, and a twin-XL mattress is 39 inches by 80 inches. Two twin-XL beds side-by-side are the same size as a standard king mattress.
A California king mattress is narrower than a typical king mattress, but it is 4 inches longer, which makes it ideal for people who are tall.
The twin-XL mattress is 5 inches longer than a standard twin mattress, but it is the same width. It is the same length as a standard queen or king mattress. This mattress is ideal for tall adults and teens.