Learn more about mattress sizes and make sure to get the mattress that’s the right size for your needs. Full, or double, mattresses are great for your child s room since the extra width compared to a twin mattress means your child will have more room to stretch as he/she grows. A Serta queen mattress measures approximately 60 x 79.5. King mattresses are a great solution for the master bedroom, as the extra room can create a more luxurious sleep experience. Do we buy a King or Queen size mattress and bed? After a savvy sales pitch and a fifteen-minute proclamation on his wife, three offspring and French poodle named Harry, he gave us his personal mattress views on the King vs Queen. You’ve decided on a king size bed, simple enough. California King or Western King beds are 12 wider than a Queen and 4 longer. Compare Twin vs.