What's the difference between a bunk bed and a loft?

Bunk bed sets consist of two beds stacked on top of each other. A loft bed uses the same concept, but instead of putting a second bed on the bottom like a bunk bed does, a loft bed uses that space for another purpose. Some loft beds have an open space where the bottom bunk would go, and others have built-in furniture, such as desks.

What size mattresses should I use for a bunk bed?

Some bunk beds have two identical twin-size mattress frames, and others have a larger full-size frame on the bottom and a smaller twin-size frame on the top. Bunk beds rarely accommodate larger mattresses than full size, and for stability reasons, the larger mattress is typically on the bottom.