How do I know what springs should I buy for my garage door?

To pick the right springs, first identify which type you have. If the spring sits horizontally on a metal shaft above the door, you have torsion springs. If two long springs run parallel to the horizontal tracks on each side, you have extension springs. Next, weigh the door by disconnecting the opener and using a bathroom scale to measure the bottom edge as you slowly lower it. Record the door height and width too. For torsion springs, you will need the wire diameter, inside diameter, and length, all stamped or measurable on the existing spring. For extension springs, match the color code and length. Always buy matching springs in pairs and order from the same manufacturer. Replacing only one always shortens the life of the other.