Measure the curtain track from the left edge to the right edge with the tape measure, and write the measurement down on the paper.
Multiply this width measurement by 2.25. For example, if your curtain track is 65 inches long, multiply 65 by 2.25 to get a total of 146.25.
Divide the number determined in Step 2 by the width of the fabric. Most decorator fabric is 54 inches wide. Round your answer up to the nearest whole number. For example, 146.25 divided by 54 equals 2.708 . This rounds up to 3 and is the number of fabric widths you need.
Measure the length of your drapes. Position the tape measure about half an inch above the top of the curtain track, and extend the tape measure straight down to the floor. Add 16 inches to this length to enable you to create the heading and hem of the curtain; this is your cutting length. For example, if the height measurement is 80 inches, 80 plus 16 equals 96 inches.
Multiply the width number by the cutting length to determine the total fabric yardage. Divide this by 36 to find the yardage. For example, multiply 3 by 96 by equals 288; 288 inches divided by 36 equal 8 yards.