To determine the size of windshield shade you need, you can follow these steps:

1. Measure the width and height of your windshield. You can use a tape measure to get accurate measurements.

2. Check the size chart provided by the manufacturer of the windshield shade you are interested in. Many manufacturers provide a size chart that lists the dimensions of their shades and the corresponding vehicle models they fit.

3. Compare the measurements of your windshield to the size chart to determine which size shade will fit your vehicle.

4. If you are unsure which size shade to choose, you can try a few different sizes until you find one that fits properly. Some customers have reported that car sunshade sizes are arbitrary and that it may take some trial and error to find the right size.

5. Keep in mind that some windshield shades are adjustable and can be resized to fit a variety of vehicles. For example, the EzyShade Windshield Sun Shade is made up of two identical rectangular shades that can be installed vertically or horizontally to achieve the perfect fit.

Overall, the best way to determine the size of windshield shade you need is to measure your windshield and consult the size chart provided by the manufacturer of the shade you are interested in.