From the middle of the 19th century up to the start of World War I, iron beds were handmade across the United States. Beds during this time had no standard sizes. Instead the beds were typically sold with a set of springs and were covered with a pallet made of feathers or straw. If you find an antique bed in an attic, an estate sale or even at a junk yard, you must convert it to accept a standard mattress before using it.
Attach a set of bed converter rails specifically made for antique iron beds to the headboard and foot boards. The rails must have antique iron bed fittings. Antique beds used different fittings than modern beds. If you purchase modern bed converter rails, they will not fit onto an antique bed. The more common size of bed headboards and footboards was similar in size to queen-sized beds. If you purchase a twin-sized mattress for your antique bed, it may seem to small. By contrast, a king-size bed mattress may seem too large.
Measure the length and width of the antique bed rails. The width of bed rails are measured differently based on whether they resemble an upward facing L shape or a downward facing L shape. An upward facing L-shaped bracket is designed to hold bed slats. For this type of bed rail, measure the width of the bed at the head, midpoint and foot. Subtract 1/2 to 1 inch from the narrowest point for clearance.
Measure the width of the bed from the outside of the rail on one side to the outside of the rail on the other side at the head, middle and foot of the rail, if the bed frame has brackets that resemble a downward facing L shape. Subtract the width of the rail, which is usually 1 1/2 inches for clearance. To measure the length of the bed, take the measurement from the headboard to the foot board and subtract 1 1/2 inches to make room for blankets and a comforter. Measure the height of the bed from the bed rails to the top of the foot board to determine the mattress clearance size.
Insert two-by-four bed slats meant for a standard queen into the bed rails spaced 1 foot apart from the foot to the head of the bed to support the bed.
Place a low-profile box spring and a standard queen mattress on your bed. Place the box springs directly over the bed slats so that the head and foot board of the bed are centred. Place the mattress over the box springs so that the head and foot board are centred. Antique iron beds may appear dwarfed if you use a full-sized queen box spring and pillow-top mattress. Avoid king-size and California king-size bed mattresses. These mattresses will dwarf your antique bed frame.
If you do not wish to convert your bed to a queen-sized bed, you may purchase a custom-made mattress that will fit your antique bed's current size. Order the mattress and box spring using the measurements that you took in Step 1. If your head- and footboards are an unusual size, such as wider or shorter, you may choose to use bed slats and a mattress for a twin- or king-size bed.