A king size bed measures 76 inches wide by 80 inches long. It is the widest standard mattress size available, although some companies manufacture oversize and custom beds that are wider. The surface area of a king size bed is 6,080 square inches, which is larger than other mattress sizes. King size beds are an excellent choice for couples looking for space to spread out, as well as people who sleep with their children or pets. Keep in mind that king size beds require significant space, and some bedrooms may not have enough square footage for a king size bed.