How To Measure A Spring

How To Properly Measure a Spring

When a door quits behaving—slams shut, creeps open, or won’t budge at all—the culprit is usually a tired spring. Measure it right the first time and the fix is painless; measure it wrong and you’re stuck wrestling with the door again next week. After 35 years shipping springs to car washes, fleet shops, and farm yards in every kind of weather, we’ve boiled the process down to six practical steps that work in the field, not just on paper.

1. Identify the spring style

• Torsion – mounted on a shaft above the door.

• Extension – stretched along the horizontal tracks.

Everything that follows assumes you’re replacing a torsion spring, the most common counter-balance on commercial doors.

2. Measure the wire size

Grab a tape measure or calipers and count 20 coils. Measure that distance in inches, then divide by 20.

3. Measure the inside diameter (I.D.)

Use a caliper if you’ve got one; otherwise measure across the spring and round to the nearest ¼-inch. Commercial doors most often use 2”, 2 5⁄8”, 3 ¾”, 5 ¼”, or 6” I.D. coils. Anything oddball? Call us or send us a message, we’ve seen it.

4. Measure the relaxed length

Unwind all tension, let the spring sit flat, then measure tip-to-tip excluding the cones. Do not measure it under tension, you want this measurement to be unwound.

5. Note wind direction

Stand inside the door.

• Left-wind spring lives on the right side of center and the end of the wire points left.

• Right-wind spring lives on the left side and the end of the wire points right.

Write it down; it matters.

6. Record the finish

Galvanized stays clean; oil-tempered is a bit more cost effective but can rust over time. We stock both.

Turning measurements into a part number

Put those numbers in the same order every time—I.D.  ×  wire size  ×  length—and you’ve got our catalog code.

Example: Oil Tempered Spring that's left hand wound with 2” I.D. × .243” wire × 46” length → Part # SPO2-243-46LH-C

The -C at the end indicates it ships with cones. We ship all springs with cones when ordered at American Door Supply.

That number links straight to the product page on our site, so there’s no guesswork when you’re ordering before the 4 p.m. shipping cutoff. 

Two quick safety reminders

1. Unload the spring completely before you pull it off the shaft. One full turn of tension can break knuckles—ask any tech who’s been there.

2. Always replace both springs on a pair. If one failed, the other isn’t far behind.