A folding bed frame includes standardized right and left bed frame assemblies that are connectable by central connecting bars to form an adjustable bedboard frame that fits mattresses of differing widths. The bed frame is easy to transport when disassembled into the separate frame assemblies that are each less than half the width of a conventional frame for a double bed. The smaller and standardized frame assemblies reduce manufacturing cost. Foot brackets are pivotally connected to the bottom of the bedboard frame under each bed frame assembly and support the bedboard frame and mattress. Each central connecting bar has U-shaped slots on its ends that clip over the inner side edges of the right and left bed frame assemblies. Each frame assembly has a hinge at its middle axis at which a lower half folds over onto an upper half to allow the assemblies to fit in a packing box.