Twin mattresses are 39 inches wide and 75 inches long. Double mattresses are 15 inches wider at 54 inches wide and 75 inches long.
Often used in the rooms of children, twin beds take the least amount of space in a room. Double mattresses provide additional space for the single sleeper, and they give kids more comfort as they grow.
While double beds are 15 inches wider than twin beds, couples may not find double mattresses wide enough. They provide only 27 inches of width per person.
Double beds were the most common choice for couples until the 1960s. It's then that queen and king size mattresses became popular.
After Little Ricky was born on "I Love Lucy," some thing changed. Producers decided that, although they were married, Lucy and Ricky should sleep in separate twin beds in order to downplay any suggested sexual relationship.