The largest standard mattress size is the king bed. King mattresses are 76 inches by 80 inches and considered the most popular size for couples because of the personal luxury space it provides. Be aware that a king size isn’t for everybody. King mattresses cost the most because they contain more materials compared to other mattress sizes. Plus, they’re difficult to move and only fit inside master bedrooms at least 13 feet by 13 feet or larger—placing a king bed inside a smaller room may make you feel cramped in your bedroom. But, if you’re single and have the floor space and the money to enjoy a king size mattress, go for it.