Performance Signs manufactures magnets up to 24 inches high, and there is no limit on magnet length. However, we recommend your magnetic sign does not exceed 18 x 24 inches in size. Larger magnets are too weighty to adhere snugly to your vehicle.
Based on our experience, a set of two 12 x 24-inch magnets works well for most trucks, cars and vans. This standard size is lightweight enough to stick tightly while providing a high-visibility advertisement for both sides of your automobile.