Cover a prong-style upholstery button with a fabric that complements or matches the fabric of the ottoman. Cover enough buttons for your entire ottoman top. You can often take fabric to a local upholstery shop and they will cover your prong buttons for you using a machine.
Turn your ottoman upside down and open the underside of the ottoman so that you can see the top board of the ottoman. Lidded ottomans are very easy; simply remove the lid. Place a large piece of paper over the top of your ottoman.
Measure the width of the ottoman, divide that in half and draw a line. Measure the height, divide it in half and draw a line. The intersection of the lines will give you the position of the center button. Divide the top half in half and draw a line. Repeat this for the bottom and both sides. You should have four lines equidistant in each direction. Mark the four intersections of the second set of lines. You now have five button spots in an arrangement that should look like a five on a playing die. For ottomans 24 inches square, five tufts should be enough.
Place 1-inch graph paper on larger ottomans and space vertical rows 4 to 6 inches apart and horizontal rows 4 to 6 inches apart. Buttons are spaced evenly every other row on every other line. Spacing on the top row might be 1, 3, 5, 7, 9, on the second row, 2, 4, 6, 8, and on the third row, 1, 3, 5, 7, 9. You should stop and start with your longer rows.
Tape your paper to your ottoman and press your finger at the center button mark. Drill a small hole at your center button position (try to hold the fabric pressed down close to the hole). Drill through the wood that forms the top of the ottoman.
Remove the washer from the prong button. Press the fabric-covered prong button through the fabric and wood until it is snug against the wood. Insert the washer from the back or underside of the ottoman lid or board. Slide the washer over the prongs and spread the prongs to hold the button in position. Repeat for all of your buttons. Only drill one at a time as your fabric will move with each tuft.