How to Measure a Garage Door Torsion Spring
Four numbers identify a torsion spring completely: wire size, inside diameter, length, and wind direction. All four can be taken with a tape measure and ten careful minutes — and having them means we can quote accurately and arrive with the right spring on the truck, before anyone drives out.
This page exists to make your service call faster, not to turn spring work into a DIY project. Measuring below is safe; loosening a winding cone is not — that part is always technician work.
Everything on this page is done with a tape measure on a spring you never touch with a tool. Do not loosen the set screws on a winding cone, do not put a winding bar into one, and do not try to unwind a spring that still has tension. The energy stored in a wound spring is the whole reason spring repair is technician work.
Wire size — the 20-coil method
Wire size is the thickness of the steel the spring is wound from, and it is the measurement people get wrong most. Common sizes sit within a few thousandths of an inch of each other, so no eyeball test works. The field method is to measure a row of coils and look the size up on a chart:
Pick a stretch of spring where the coils sit tight together, away from the cones. Count out exactly 20 coils, mark the start of the first and the end of the twentieth, and measure between the marks to the nearest sixteenth of an inch. Then do it again — the count is the part everyone rushes.
| Wire size | 10 coils measure | 20 coils measure |
|---|---|---|
| .207 | 2 1/16 in. | 4 1/8 in. |
| .2187 | 2 3/16 in. | 4 3/8 in. |
| .2253 | 2 1/4 in. | 4 1/2 in. |
| .2343 | 2 5/16 in. | 4 5/8 in. |
| .2437 | 2 7/16 in. | 4 7/8 in. |
| .250 | 2 1/2 in. | 5 in. |
| .2625 | 2 5/8 in. | 5 1/4 in. |
| .273 | 2 3/4 in. | 5 1/2 in. |
| .283 | 2 13/16 in. | 5 5/8 in. |
So 20 coils at 4 1/2 inches is .2253 wire; 20 coils at 5 1/4 inches is .2625. If your measurement lands between rows, re-measure before picking the closer one — the spacing between sizes is exactly where sloppy counting shows up.
Inside diameter
Measure straight across the open center of the coil — the hole the shaft passes through, not the outside of the spring. Residential springs are usually 1 3/4 inches, 2 inches, or 2 5/8 inches. Check the cones before reaching for the tape: many carry a stamped or cast number, where 175 means 1 3/4 inches, 200 means 2 inches, and 258 means 2 5/8 inches.
Length
Measure the coiled body of the spring from end coil to end coil, excluding the cones at both ends. The number is only honest when the spring is unwound — a spring under tension stretches, and a stretched measurement undersizes the replacement. If the spring is broken, this gets easy: measure both pieces and add them together.
Wind direction
Torsion springs come in right-hand wound and left-hand wound, and a two-spring door uses one of each. The convention: standing inside the garage looking at the door, the right-hand-wound spring usually sits left of the center bracket and the left-hand-wound spring on the right. Cones follow a color convention too — red for right-hand wound, black for left — but paint is a hint, not proof. To be certain, look at the end of the coil: if the wire runs upward and away clockwise, it is right-hand wound.
If that last check sounds fiddly, it is — a clear photo of each spring end, sent through the estimate flow, answers it for you.
The six classic mistakes
Common sizes differ by a few thousandths of an inch. Two springs can look identical and behave very differently — measure coils, don't eyeball.
Coils spread apart where the spring meets the cone. Measure a clean section where the coils sit tight together.
The spec that matters is the inside diameter — across the open center of the coil, not edge to edge over the wire.
Spring length means the coiled body only, end coil to end coil. The winding and stationary cones are hardware, not spring.
A wound spring stretches longer on the shaft. Length is only accurate unwound — another reason this measurement pairs naturally with a broken spring.
Red and black winding cones usually mark wind direction, but paint fades and gets swapped. Confirm the coil direction itself.
A spring is not a stronger-is-better part
Wire size, diameter, and length trade against each other, and the combination has to match the door's weight and height — a thicker wire on the wrong length can leave a door heavier at the floor than the old spring ever did. That is why we size replacements off the door itself and why these four numbers are worth having before you call: they turn “my spring broke” into a conversation about the exact part your door needs.
What IPPT means — and why each measurement changes it
IPPT stands for inch-pounds per turn: the amount of torque the spring adds to the shaft for each full turn of winding. A door needs a specific total torque to balance its weight, and that total is IPPT multiplied by the number of turns. Change any one of the three physical measurements and you change the IPPT — which is exactly why the four numbers above have to be recorded accurately, not estimated.
| Change | Effect on IPPT | Practical meaning |
|---|---|---|
| Thicker wire | IPPT increases | Spring rate scales roughly with the fourth power of wire diameter, so a one-step change in wire size is a much bigger jump than it looks on a ruler. |
| Longer spring | IPPT decreases | More active coils make the spring less stiff, so each turn of winding adds less torque. |
| Larger inside diameter | IPPT decreases | A bigger coil diameter reduces the spring rate when wire size and coil count are unchanged. |
| High-cycle conversion | Must be re-matched | See below — larger wire is usually paired with added length so the door still gets the torque it needs. |
This is also why a thicker spring is never a simple upgrade. Swap in a heavier wire size without re-engineering the length and the door will fight the opener on the way down and slam on the way up. The three dimensions move together or not at all.
Why high-cycle springs are thicker and longer
Standard residential springs are rated for roughly 10,000 cycles — about seven to ten years of normal use. High-cycle springs, rated for 25,000 to 50,000 cycles or more, usually achieve that lifespan with a larger wire size, because thicker wire runs at lower stress and resists fatigue. The catch: thicker wire alone would push the IPPT well past what the door needs.
So a correctly engineered high-cycle spring is also longer than the standard spring it replaces. The added length brings extra active coils, which bring the IPPT back down to the value the door requires, while the thicker wire provides the longer service life. Length alone does not create cycle life — it is the combination of wire size, coil diameter, active coils, and required turns that does — and the finished spring still has to fit the shaft and produce the right torque. That engineering is the difference between a high-cycle conversion and a guessing game.
Common questions
What does IPPT stand for?
Inch-pounds per turn — the torque the spring adds for each full turn of winding. The door needs a specific total torque to balance, and that total is IPPT times turns. Thicker wire raises IPPT, longer springs lower it, so replacing one dimension without re-checking the others unbalances the door.
Is it safe to measure a torsion spring myself?
Measuring is safe; adjusting is not. Reading coil counts, diameters, and lengths involves a tape measure and nothing under your hands. The line you do not cross is loosening the set screws on a winding cone or putting a bar into one — that is where the stored energy lives, and that is technician work.
My spring is broken. Can I still measure it?
Yes, and a broken spring is actually easier to measure accurately — it is fully unwound, so the length reading is true. Measure both pieces of the coil body and add them together.
What do the numbers stamped on the cones mean?
Many cones carry a casting number for the inside diameter: 175 for 1 3/4 inches, 200 for 2 inches, 258 for 2 5/8 inches. It confirms one of the four measurements, but not the other three — wire size, length, and wind direction still need measuring.
Can a slightly different spring size work?
Springs are engineered as a set of trade-offs between wire size, diameter, and length, and a thicker wire is not a stronger upgrade — it changes how much torque each turn of winding adds. A replacement has to be sized to the door's weight and height as a system, which is why we measure the door rather than copy the old spring's label: the label is only right if the last installer sized it correctly.
Why do you ask for these numbers before a visit?
Because the right spring on the truck is the difference between one visit and two. A homeowner who can tell us the wire size, diameter, length, and wind direction — or send clear photos through the estimate flow — lets us arrive with the correct part already in hand.
Start at Square One.
Tell us what your garage door is doing. You do not need to diagnose it before you call.