Place the end of the tape measure at one top edge of the ottoman and stretch it straight across the widest part of the top of the ottoman to the opposite edge. Repeat the process from another point on the top edge, to ensure accuracy. If the measurements vary, use the widest diameter measurement and add 1 inch for seam allowances; write it down.
Measure the height of the ottoman by placing the end of the tape measure at the top edge and stretching the tape measure straight down to the bottom edge of the ottoman where you want the upholstery fabric to end. Add 1 inch to the height measurement for seam allowances and write it down on the paper.
Stretch the tape measure around the ottoman one complete time to measure the circumference. Add 1 inch to the circumference measurement for seam allowances and write down the circumference, too.