Twin

• A twin-size mattress, the smallest adult mattress, is also known as a single bed. It measures 39 inches wide by 75 inches long. A twin mattress is ideal for a single individual or children's room. An XL twin, common in college dorm rooms, measures 39-by-80 inches to accommodate taller adults comfortably.
  
  

Full

• A full, also known as a double-sized bed, measures 54-by-75 inches. A full-size is ideal for two small individuals or a single person who desires more space than offered by a twin. A drawback to the full-size is that, when shared, each person only has 27 inches of space--much less than the 39 inches offered in a twin.
  
  

Queen

• Measuring 60-by-80 inches, a queen-sized bed is the next step up from a full. It offers each individual 30 inches of width when shared and is more accommodating to tall individuals with its extra 5 inches in length. Most couples can comfortably fit in a queen-sized bed, although larger individuals or those who like to stretch out may desire additional space.
  
  

King

• The largest bed size is the king, which measures 76-by-80 inches, giving each individual 38 inches of width and accommodating taller adults. Kings offer the most space for couples to stretch out and have their own space. If you are extra tall, you may opt for a California king instead, which takes 4 inches from the width and adds it to the length. California kings are 72-by-84 inches.