Rain-X offers a blade size finder on its website where you can search based on the year, make, and model of your automobile. If you're unsure of what blade size you need, try looking in the owner's manual or search for your vehicle blade size online. Blades that are too long can hit each other and cause damage to the blade mechanism. Choosing a blade that's too short can leave large areas of your windshield unaffected, lowering your visibility. Blades on the driver's side extend longer than the passenger side to provide the best visibility for the person behind the steering wheel.

Wiper sizes are indicated in millimeters, noting if the wiper set is for the front or rear of the car. Once you find the correct measurements, you can purchase vehicle-specific blades or find general blades that match the length required for certain automobiles. Most experts recommend sizing your blade as close to the manufacturer's instructions as possible to maintain safe driving conditions. Wiper blade sizes are designed to cover a certain area of your windshield to provide maximum visibility in stormy weather.