What Are the Dimensions of a King Size Mattress?

Jared Huizenga

You might enjoy sleeping with, but not right next to, another person. Or perhaps you’re a tall person and just need more room to spread out. If so, a king size mattress might be the right size.


A king size mattress is 80 in. long, the same length as a queen size mattress and five inches longer than a twin or full size mattress.


King size mattresses are nearly as wide as they are long, measuring 76 in. wide. This makes them 16 in. wider than queen size mattresses, 22 in. wider than full size mattresses, and 37 in. wider than twin size mattresses.


The depth of a king size mattress varies, depending on the manufacturer and style; pillow tops, for instance, are larger than firm mattresses. King size mattresses can range in size from 5 in. deep to 20 in. deep.


The one exception to the size of king size mattresses is the California king size mattress, which is longer and narrower than a standard king size mattress. A California king is 72 in. wide and 84 in. long.


Many people think that two twin size mattresses are the same as a king size mattress. Standard size twin mattresses are 5 in. shorter than king size mattresses.