Also be sure to measure the bed frame, if you already have one. This will also need to fit within the headboard. The general rule when measuring the height of the headboard is this: measure half way up the wall of the room where the headboard will be placed against. Your headboard should never exceed this height! Try to find a headboard that either reaches half way or down to a few inches below that point. This will prevent the headboard from "crowding" and overpowering the room.
Let’s talk about measurements. Now, double beds can be a bit tricky, since depending on the brand, style, or manufacturer, there may be different widths and lengths. It is imperative that you measure the actual mattress and box spring before looking for a headboard. Seeing a headboard that is made for a "double bed" does not necessarily mean that it will fit YOUR double bed.