Buying a too-small mattress is one of the biggest mistakes new bed-buyers make. Couples who've been sleeping on a "double" since they got married may think that's just fine, until they learn that each person has only as much sleeping space as a baby's crib! Here are size guidelines for shoppers from the Better Sleep Council:

Full beds, sometimes still called "double," are 53 inches wide, which is just 15 inches wider than a twin size (single). That leaves each partner only 27 inches of personal space, or about the width of a crib. Both twin and full sizes are approximately 75 inches long, which may be too short for some adults, especially men.

Recommendations: Full size is only enough space for a single sleeper and only if under 5 feet 5 inches tall. Parents are increasingly choosing full size over twin for teenage bedrooms, and even for younger children in order to give parents a more comfortable place to rest when reading together at tuck-in time.

Queen beds are 60 inches wide by approximately 80 inches long – 6 inches wider and 5 inches longer than a full size mattress. These added inches can make all the difference in comfort, especially for couples, and have made the queen today's most popular mattress size. However, with 30 inches of personal space, each adult still has 9 inches less width than if they slept alone in a twin bed.

Recommendations: Queen size is a good choice for guest rooms, smaller master bedrooms and for couples who prefer close quarters. It's also a great choice for single sleepers who are also "sprawlers."

King beds are 76 inches wide by approximately 80 inches long – about 18 inches wider than a queen. This is the closest a couple can come to having as much personal space (38 inches) as each would have on a twin bed. In fact, two twin extra-long beds pushed together are about the same size, an option that can offer a flexible arrangement for a guest room.

**For consumers on the west coast, there is also the "California King," which is 72 inches wide by 84 inches long – 4 inches narrower and 4 inches longer than a regular king.

Recommendations: King size is the best choice for couples that want maximum personal sleeping space. It's also the best bet to accommodate that time on Sunday morning when children may pop into bed – or if the pets in your house have mattress privileges! However, size can be a problem. Even with a "split box spring" – two twin-size foundations to support it – to make a king set more manageable, it may be too big for some bedrooms or too bulky to navigate through some corridors, doors and stairwells. It's a good idea to break out the tape measure if there is any doubt.

Mattress size chart

(All dimensions may vary by +/- one half inch)