Dimensions
The dimensions of a full-size box spring vary depending on whether it's a low- or high-profile version. The lower versions are approximately 5 1/2 inches in height, while the high-profile version is a standard 9 inches in height. The difference between the low and high profiles is purely ascetic. The width of a full-size box spring is 53 inches, just 15 inches more than a twin, or single size.
Purposes
According to Dimensions Guide, in general, full-size box springs serve three basic purposes. They work to create a flat surface, sturdy enough to place a mattress on top, act as shock absorbers, and help raise the mattress height, making it easier to get in and out of bed. A full-size box spring also helps to expand the surface area and provides further support.
Other Considerations
At 75 inches long, a full-size box spring is the same length as a twin size. This measurement, however, is often the deciding factor when choosing between full and queen-size box spring sets, (a queen-size bed is 80 inches long). This relates particularly to men, who are typically taller. If sharing a full-size bed, each person would have 27 inches to themselves, which is the approximate width of a baby crib.