Single car garage doors come in a range of sizes from 7ft. to 10 ft. wide and from 7-10 ft. tall. Commercial doors can be much larger. The number of springs required depends on the weight of the garage door. The springs must be strong enough to counterbalance the doors weight to properly lift and close door.

If a broken spring needs to be replaced, then you first have to measure the existing broken spring on the door.

If you have a custom wood garage door than it is most likely to have more than one spring. Basic metal garage doors with no insulation or windows will almost always have only one spring.

If you have a solid one piece flip up door than the concept is the same. U just use extension springs.

Once I replaced a garage door that had no springs at all. This is because it was made out of fiberglass and weighed almost nothing. I have only seen one of these doors in 12 years. It was also in California where weather is always mild.

A professional technician should handle all repairs that involve springs. The danger of serious injury is too great for the average person.