The standard length for a king-size mattress is 80 inches. This is the same length as a queen-size mattress, but a king is 16 inches wider than a queen.
King-size beds are recommended for people who prefer extra width when they sleep. A king-size mattress is the same width as two extra-long twin beds combined, and it offers the most sleeping area of any bed size. Many people opt for a queen over a king, since king-size beds are large and take up a lot of space in a bedroom.
The California king sacrifices width for length. It is 72 inches wide and 84 inches long. This size is ideal for taller people.