80.71''W x 31.5''D x 14.57''LWould that be close to a full sized bed or less?
A full sized bed is a double bed, the one that comes between a twin bed and a queen bed size. The largest bed of course, is a king sized.
Your bed appears to be closest to a Twin Extra Long though the narrow width suggests it is likely a cot. For sheet shopping I would suggest the twin XL. There will be a little extra to tuck but it should work fine. Standard bed sizes vary slightly by manufacturer but here are the basic sizes. Mattress depths vary from 4 to about 22 TWIN3975 TWIN XL (TYPICAL DORM)3980 FULL5475 QUEEN6080 KING76-7880 CALIFORNIA KING7284
