First, think about the sleep footprint you'll leave. Will the footprint include one body or two? Are those bodies small? Big? Tall? Short? A combination? Take note of the amount of space you, or your and your partner, will take up, and then add some extra space - nobody wants to be right up against the edge of the bed feeling like they're about to roll off. If the person sleeping in the bed tends to move a lot during sleep, you should add even more margin. Also, keep in mind that mattress measurements are slightly less than standard bed size, to ensure the mattress fits inside the frame.
Here's our rundown on the different mattress size options and what each one is best for.
Size: 34" x 74"
Good for: Kids' bedrooms, smaller guest spaces, daybeds
Small Double Size
Size: 47" x 74"
Good for: College dorm rooms, small apartments
Size: 54" x 74"
Good for: Small guest rooms, single sleepers who need more space
Size: 60" x 80"
Good for: Couples, guest rooms,Master bedrooms
Size: 70" x 80"
Good for: Master bedrooms,Couples with different sleep preferences