When ordering torsion springs there are 4 specific items you will need in order to get the correct replacement spring. Those items are the wire size, inside diameter of the spring, length of the spring, and the wind of the spring (right or left wound).
A spring's wire size can be determined by using a caliper, micrometer, or wire gauge. If none of these tools are available, simply measure ten coils of wire to the nearest 1/16th of an inch, and refer to the Spring Wire Chart here. The spring must be tightly compressed, with no gaps. Still unsure how to properly measure a spring? Register for Solution Education and purchase the ‘How to Measure a Spring’ video tutorial.
First, measure the inside diameter to the nearest 1/16th of an inch. For springs with cones inserted into the ends of each spring, the cone likely will have a manufacturers name (OHD, Raynor, etc.) which will give you a clue toward the proper identity. The chart available here shows the most common ID's used by various manufactures. If no manufacturers name is evident, usually a part number on the cone will indicate the ID.
First, measure the spring length in an unwound state. The spring must be tightly compressed, with no gaps. In the case of a distorted or broken spring, simply count the total number of coils and multiply by the wire size.
To ensure the correct wind, please refer to the Winding Chart below. Please remember the side of the door the spring is located on does not indicate the wind of the spring. Most winding cones are color coded for hand identification. Right hand wound springs should have red winding cones while left hand wound springs should have black winding cones. See illustrations here.