King

A king measures 76 by 80 inches: the same length as a queen, with 16 more inches across. Split between two people that is 38 inches each, exactly the width of a twin mattress. This is the clearest way to picture what the extra money buys.

Width changes how the bed behaves rather than just how it looks. Two sleepers turn over without touching, motion from one side arrives faintly on the other. A child or a dog joins without anyone losing their place. Couples on different schedules feel it most, since a partner leaving at 5 in the morning no longer moves the whole mattress.

Rooms have to earn it. A king needs roughly 12 by 12 feet before it stops dominating. You want 24 to 30 inches of clear floor on both sides and at the foot for walking and for changing sheets. Measure the doorway, the hall turn and the stair landing first. At 76 inches, this is the width that most often has to be stood on end or fed through a window.

Costs scale with the surface. King sheets, duvets and protectors carry a premium over queen, and the mattress is heavy enough that rotating it takes two people. Many kings sit on a two-piece split foundation, which solves the delivery problem but means checking that your frame supports both halves.