A box spring is basically a bed base that is placed on top of a wooden or metal bed frame which sits on the floor. The box spring is the same size as the mattress placed above it. Combined, the frame, box spring, and mattress make up a bed.
The purpose of the box-spring is to raise the mattress' height, making it easier to get in and out of bed and to create a flat and firm structure for the mattress to lie upon.

With the increasing height of mattresses, manufacturers now make box springs (foundations) in different heights. Standard "high profile" box springs are 9" in height, whereas "low profile" box springs are 5½" high. This makes it easier to get in and out of bed. The difference between the two heights is purely aesthetic and makes no difference in the support provided for the mattress.

Question: What are the measurements of a split queen box spring?
Answer: Each half of the split queen box spring measures 30 x 80 for a total width of 60 inches and a total length of 80 inches.