Measure the width of the ottoman across the top. Also measure the depth of the ottoman across the top. Record the two measurements. For example, if your ottoman is a 30-inch square, write 30 by 30 inches.
Add 1 inch to the depth and width measurements. For example, a 30-inch square ottoman plus 1 inch is 31 by 31 inches.
Measure the height of the ottoman, and record the measurement. Two sides of the ottoman will be the depth by the height, for example, 30 inches by 15 inches, and two sides will be the width by the height, for example, 30 inches by 15 inches.
Add 1 inch to each of the measurements for the seam allowances.
Multiply this measurement by 2, and add the total to the depth of the ottoman with the seam allowance. For example, for the 30-inch square and15-inch high ottoman, you'd end up with a measurement of 63 inches, meaning you would need almost 2 yards of fabric that is at least 45 inches wide to cover the top of the ottoman and two sides.
Add the measurements for twice the height of the ottoman with the seam allowance. For a 15-inch high ottoman, the sum would be 32 inches. You'd need an additional yard of 45-inch fabric to cover the two remaining sides of the ottoman.
Add 1 yard to the fabric calculations if you are using a printed fabric so that you can match the patterns.