Shaker Tape Yardage Formula To determine the correct amount of yardage needed, use this formula: Measure the front rail between the posts. Measure from the center of the back rail to the center of the front rail. Multiply these together. Divide the resulting figure by 9, and that's the total number of yards of 1" tape required. NOTE: If you want to use two colors, order half the total number of yards per color.