Lay the headboard on a flat work surface in front of you horizontally. Use a tape measure to measure a width of 18 inches on each. Mark it with a piece of chalk.
Cut the headboard down to an 18-inch width, using an electric saw. This is the standard size for a bench.
Place two step stools 2.5 feet apart. Adjust them so they are perfectly parallel to each other. Place the sawed-off headboard on top. Straighten it so it lines up exactly with the step stools.
Nail the headboard into the step stools, inserting two nails, spaced 6 inches apart, into each stool.