Springs come in a multitude of different sizes. The size of the spring is determined by the weight and the height of the door. This is what balances the door when you open and close door.
All springs are sized by the wire gage and the length and diameter of the spring.
Some garage doors will have 2 springs and they can be different sizes so each spring should be measured individually. Springs are measured and stamped on the spring as follows.
Example: (.207 x 1 ¾ x 28) .207 = wire gauge, 1 ¾ =diameter, 28 = length of spring. Extension springs used on a solid one piece door are measured somewhat similar. These springs almost always have a sticker on it that has the size printed on it. They are measured as follows.
The numbers start at 300 and go up to 900.
The most common size is 728(700=wire gauge, 28=length of spring). A 300 series is a heavy duty spring and 900 series are lightweight springs.
Extension springs for a sectional door are measured in color coding and length of spring.
The color painted on spring determines the wire gauge and whatever the length of spring is.
Determine the spring size
Whenever I cannot determine the spring size just by looking at door and from experience. I have to remove the old springs and make my measurements on all springs to make sure they match what was on the door. You can’t measure a spring correctly if it is wound up under tension. When a spring is wound up it will stretch about 2 inches longer
If you had to measure your spring yourself you can measure 9 inches of spring and count the number of wires within the 9 inches . This will give you a wire gauge size without having a tool that measures wire thickness. Then measure length of spring without adding the silver metal ends or spring. These are called the cones and they screw into the ends. If spring is broken just put both broken pieces together when you measure length. Then measure how wide the circle of spring or diameter