With a standard shower curtain height at 70 or 72 inches, adding a few inches will give you a good indication about your shower curtain rod height. With a standard shower curtain of 72 inches long, the curtain rod should be installed around 75 to 77 inches from the floor.
Most standard shower curtains are 72 inches square to fit a 6-foot tub. If you want a larger or smaller curtain, simply add 8 inches to the finished width and 16 inches to the finished length to cut the rectangle and figure yardage.
A standard shower curtain measures 72″ x 72″ when finished, and the fact that I wanted to make a white shower curtain made it very easy for me in the fabric measurement department: I used two cuts of Kona Cotton that measured 4 ½ yards each.
Measure the width of the entire space the curtain will fit over. This typically is the front section of the shower or bathtub. Measure in inches, then choose a rod that fits the opening. Keep in mind that standard shower curtains are 70 or 72 inches wide.