A standard garage door generally has two garage door springs in the system. But the number is not fixed. You need at least two springs in your system. A large door needs more springs. The quality of the spring must vary according to the size of the garage door, and the weight that the spring must support. From the experience of Los Angeles Garage Door's chief garage door technician, garage door springs can range in length from 15 to 50 inches, although there are always exceptions to the rule. LA Garage Door generally carries two types of garage door springs: galvanized garage door springs, which come with a zinc coating to help protect against rust, and black-coated garage door springs; the black-coated garage door springs are oil-tempered.
If one of the springs of your garage door is not working, then the customary advice is to replace both springs--the logic is that if one spring is not working properly, than the other spring is most likely also close to breaking.
Whatever the choice, the recommendation is that garage door customers call a garage door repairman to deal with the problem. This is because replacing a garage door spring can be a dangerous task. Garage door springs are wound very tightly; the wires have a lot of tension. A simple mistake while trying to replace a garage door spring can result in injury. Even experienced garage door technicians have not escaped injury from garage door springs when the garage door spring wrapped around their hand. Also, a garage door spring installed improperly can cause the garage door to collapse, which is also another safety issue when considering how frequently garage doors are used.