Do you need a box spring with a bed frame?

No. Most modern bed frames don't require a box spring. Frames with a built-in slat system support a mattress directly, and platform frames are specifically designed to eliminate the box spring entirely.

Whether a box spring is needed depends on the frame type. A platform bed frame or any frame with slats spaced 3 inches apart or closer provides enough support for most mattresses on its own. Older metal rail frames with no center support or slats are the exception: those typically need a box spring or bunkie board to hold the mattress. Check the mattress manufacturer's requirements too, some warranties require a specific foundation type.

Platform bed frames support mattresses directly with no box spring required.
Slat spacing of 3 inches or less is the standard threshold for adequate mattress support without a box spring.
Basic metal rail frames with no slats or center support generally require a box spring or bunkie board.
Some mattress warranties specify a compatible foundation type; skipping a box spring without checking can void coverage.
A bunkie board (typically 1–2 inches thick) works as a low-profile box spring alternative on slat or platform frames.