How wide is a king size bed frame?

A standard king size bed frame is 76 inches wide, matching the width of a standard king mattress. Some frames add 1–2 inches of overhang or border on each side, putting the outer frame width closer to 78–80 inches.

That 76-inch interior width is the number that matters most when sizing a room or buying a mattress. King size bed frames are built to hold a mattress that is exactly 76 inches wide by 80 inches long, so the frame's interior rail-to-rail measurement should match those dimensions precisely. The outer footprint depends on the frame's design, thicker side rails or decorative panels add width beyond the mattress edge.

Standard king size bed frame interior width: 76 inches (193 cm).
Standard king mattress dimensions: 76 inches wide by 80 inches long.
Outer frame width typically ranges from 76 to 80 inches depending on rail thickness.
California king bed frames are narrower at 72 inches wide, but 84 inches long.
Minimum recommended room width for a king size bed frame: 12 feet (144 inches).