To determine the size of a car's windshield wipers, measure the length of both blades using a measuring tape or ruler, or check the car's manual for specifications. It is normal for one blade to be smaller or larger than the other, so it is important to measure both.
To replace the windshield wiper blades, put the wipers in an upright position perpendicular to the hood, and remove the blades from the wiper arm. Place the metal wiper arm on a rag against the windshield to prevent scratching or breaking the glass. Attach the new wiper blade, making sure that it is secure. Repeat the process with the second windshield wiper.