Headboard height varies by style, but the width of headboards remains standard to fit four common bed sizes: twin, and twin extended; full or double; queen and king. While exists, typical headboards are 3 inches wider than the mattress's width. If you're working with a custom-built frame and non-standard bed sizes, measure the width of the bed and add 3 inches to it to determine the appropriate width for your headboard.
The full-size bed, also known as the double bed, is 59 inches wide, not quite double that of a twin bed. The length is 75 inches. A full-double headboard measures 62 inches in width.
Queen-size beds are 60 inches is typically 63 inches wide, but it varies depending on style. Given the close widths, many comforters are made to fit full/queen-size beds. A full/queen comforter is slightly shorter on the queen bed.
A king-size bed is 76 inches wide and 80 inches long. A king headboard is 79 inches wide.
Many DIY headboards follow the plus-3 inches rule; however, headboard size is a matter of personal taste, especially if you're mounting the headboard to the wall instead of the bed frame. When you don't have to consider the dimensions of a bed frame, you have more decorating options:
Chalkboard: A chalkboard headboard mounted behind a bed can be as wide as you choose. The extra width can allow space for to-do lists, motivational quotes and memos.
Tufted: Manufactured tufted headboards fit the width of the bed.
Leather: Leather headboards are manufactured to fit the width of the bed. Confining them to the bed's width -- or 3 inches added to it -- helps keep the cost down.
Fence/Planks: DIY fence- and plank-style headboards can be any width desired. Instead of a picket-fence look, try painted lattice.
Foam Board: Thicker than poster board but lighter than plywood, foam board offers some additional headboard ideas. Wrap a few layers of cotton batting around the board and cover it with fabric -- secured at the back with duct tape -- to make a lightweight upholstered headboard. Hot glue a couple of sawtooth picture hangers to the back and hang it above your bed on small nails or hangers.
Folding Doors: If you have a pair of folding closet doors that keep falling off their tracks, paint them to match your room decor and place them behind your bed for a tall headboard.
Art Headboard: Buy several large pre-stretched canvases and paint designs on them to match your decor. Hang the art behind the bed to serve as an artistic headboard. Use simple stencils and craft paint with a layer of decoupage sealer for protection, or give crayon art a try.
Rugs: Hang a large rug or several small coordinating rugs behind your bed for a headboard. Don't limit yourself to traditional hooked or woven rugs. Welcome mats can also become headboards. You may have to hang two or more together, but add some paint for a stand-out headboard.
Doors and Windows: Hang old doors or window frames behind your bed for a unique headboard. If the doors have glass inserts, remove them and replace them with mirrored tiles or a fabric-covered panel for an extra dose of color. If you're artistic, paint a scene on the wall behind a set of window frames so it looks like another view.