How wide is a twin bed frame?

A standard twin bed frame is 38 inches wide, designed to hold a 38" × 75" twin mattress with a snug fit and minimal overhang.

Twin bed frame width holds consistent across most manufacturers because it's sized to match the standardized twin mattress. The frame's outer width may measure 39–41 inches once rails and any side flanges are included, so account for that extra inch or two when measuring a room. Twin XL frames share the same 38-inch width but add 5 inches in length, reaching 80 inches instead of 75.

Standard twin bed frame interior width: 38 inches, matching the twin mattress standard.
Outer frame width (rails included): typically 39–41 inches depending on rail thickness.
Twin XL bed frame width: also 38 inches wide, but 80 inches long instead of 75.
Minimum recommended room clearance alongside a twin frame: 24 inches on each open side.