To measure the dimensions of a windshield, use a tape measure or other similar device to identify the height and width of the windshield. If the windshield is irregularly shaped, use a string to measure a side, mark the length and then compare the string to a tape measure.
Use a tape measure to determine the height and the width of a windshield. Simply hold one end of the tape measure at one corner, extend it vertically or horizontally to a corner on the same side, and then note the length of the side in inches or centimeters. Repeat this on the other side, perpendicular to the side you just measured, and record the length again.
If your windshield is irregularly shaped, you can use a string to measure the length of each side by holding the string from corner to corner and marking the length on the string. After marking the length, hold the string side-by-side with a tape measure to figure out the width. If you only have a foot ruler, lay the string out straight, and then use the ruler to count how many feet and inches long the string is by holding the ruler next to the string, marking the end and then moving the ruler forward to the marked point. Record the number of inches or feet total to figure out the length of the string, which is the length of the side of the windshield.