A torsion spring is fully described by four numbers, wire size, inside diameter, overall length and wind direction, and all four can be measured safely on a BROKEN spring without touching a wound one.
By Ryan Gold, lead technician, Reliable Garage Doors · Updated on October 28, 2026
Wire size: lay a tape along the broken spring and measure the length of exactly 20 coils, then divide by 20. The classic sizes, .207, .218, .225, .234, .243, .250, differ by hundredths of an inch, which is why counting coils beats calipers on a rusty spring. Inside diameter: usually stamped on the cone, P175 means 1.75 inches, or measured across the opening. Overall length: measure the coiled body only, not the cones, on the relaxed broken half pairs, adding both segments. Wind: hold the spring end toward you; coil ends pointing clockwise as they recede are right-wound. Left-wound springs carry red cones, right-wound black, on most brands.
The factory label on the inside of the top section usually names the door size, the spring type, the turns the springs were wound at the factory and the build date, so a photo of it is the fastest way to start a spring quote, but it is not the spring size on your door today. One label we read on a job this year printed an 8 x 7 door, SPRING TOR. (a torsion system), 7 1/2 turns, LIGHT under hardware and a build date of 09/28/05. That tells a technician what the door was built with and roughly how hard its springs were wound when new.
It does not tell anyone what the door weighs now. Twenty years of paint, an insulation kit, a replaced section or a spring someone swapped off a truck all change the math, which is why we still weigh the door and measure the spring before we quote. Measured, not guessed. Snap the label and the broken spring, text both to 757-208-1600, and leave the set screws on a wound spring alone.
From the field: see that factory label on our Facebook page.
Builders fit minimum-spec springs, previous owners fit whatever was on a truck, and doors gain weight over the years, added insulation kits, new panel sections, moisture in wood-composite doors. Copying an old wrong spring replicates the mistake for another decade. The correct method weighs the door with a scale under the disconnected door, then selects wire and length for that weight at the door’s track radius and the cycle life you want. It is exactly the arithmetic our crew runs on every spring call.
With solid measurements you can sanity-check any quote you receive, understand why two springs of identical length are not interchangeable, and recognize when a supplier is substituting a longer, thinner spring that will die young. What the numbers should not become is a DIY winding project: winding bars, cone technique and set-screw torque are where this job injures people. Measurement is homework; installation is our trade, priced on the garage door spring replacement service page with the number agreed before work starts.
Want a number, not a sales pitch? Call 757-208-1600 and we quote it on the phone where we can.
Count and divide for wire size, measure ID across the cone opening, and measure relaxed segment lengths. Those three plus wind direction fully identify the spring.
Sometimes intentional on heavy or offset doors, more often a history of one-at-a-time replacements. A weigh-in tells the truth; matched correct pairs balance best.
Doors above roughly 8 feet wide or 130 pounds generally deserve two; paired springs share load, halve the stress each and fail less violently. Single-spring economy setups on double doors are a builder shortcut.
A 10,000-cycle spring at four daily cycles lasts under 7 years. High-cycle variants cost modestly more and multiply the lifespan; ask for the math on your usage, we show it gladly.
The factory label on the top section often shows the door size, the spring type, the factory wind turns and the build date, but not the wire size or length of the spring on the door today. Use it as a starting point, then measure the broken spring or let the technician weigh the door.
