Garage door rollers come in various sizes. That means you'll need to take measurements to determine which rollers to buy if you're replacing the rollers or getting new ones. The easiest way to find out what size rollers to get is to remove the rollers currently on the garage door and measure them. If you can't get the rollers off, open the door partway so that the rollers are at eye level and you can reach them easily. Rollers come in various dimensions, but the most common sizes are 1-3 inches. To determine what size rollers you need, measure across the roller head. You should also measure the shaft or stem. Be aware that if you have an older garage door, you might need to special order rollers of a custom size. No matter what size rollers your garage door takes, make sure that the rollers are long enough. If the rollers are too short, the garage door can jump off its tracks and damage other parts of the garage door, such as the panels and hinges. Ultimately, you may have a more costly garage door repair on your hands.