Standard king size beds and queen size beds differ in width but not in length. A king size bed offers ample room for stretching out, while a queen size bed is better for smaller bedrooms. In the UK, super king size beds measure at 72 x 78, or 6 by 6.5 feet. Casper’s guide to finding the perfect size bed. The most popular mattress size around, the queen mattress fits best in a master bedroom that’s at least 10 x 10 square feet. At 76 inches wide and 80 inches long, the king mattress is large enough to accommodate couples who share the bed with their children or a sizable pet (think: a great dane).