Calculating slipcover yardage involves measuring the dimensions of the furniture you wish to cover and then converting those measurements into yards. Start by measuring the height, width, and depth of each part of the furniture piece, such as the back, arms, and cushions. Remember to include any additional length if you want the slipcover to hang over the edges. Once you have the measurements in inches, you can convert them to yards by dividing each measurement by 36, since one yard equals 36 inches. Add up all these measurements to get the total yardage you need. However, it's always a good idea to purchase extra fabric to account for errors or pattern matching. Therefore, consider buying an additional 10% to 20% more fabric than your calculated yardage.