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 July 19, 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.
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 spring 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.
