How to Measure and Size a Spring
How to Measure and Size a Spring: the decision explained before the repair, so the right service page is opened first.
What this guide answers
A wrong-size spring is the most common reason a spring replacement fails to balance. The door may still open, but it feels heavy, drifts, or wears the opener, because the spring is not carrying the weight it was sized for.
Sizing a torsion spring needs four measurements, and sizing an extension spring needs three. None of them can be guessed from the door's width alone, which is why a technician measures the old spring and the door together before ordering a replacement.
Details that matter
- Wire size: the thickness of the wire the spring is wound from. A small change in wire size changes the spring's strength significantly, so it is measured with calipers, not estimated by eye.
- Inside diameter: the diameter of the hollow centre of a torsion spring, which must fit its shaft. A spring with the wrong inside diameter cannot be fitted to the existing shaft at all.
- Length: the length of the spring when unwound and at rest. Length, together with wire size, decides how much lifting force the spring provides across the door's travel.
- Wind direction: torsion springs are wound left or right, and the wind must match the side of the door the spring sits on. A spring wound the wrong way cannot be wound to balance the door, however close its other measurements are.
- Extension springs are sized by length, wire size and colour code, and the pair must match each other. A mismatched extension pair pulls the door unevenly from the first cycle.
- Door weight and height are the final check: the spring specification is confirmed against the door it must lift, because two doors of the same width can weigh very differently depending on material and insulation.
How to use this guide
- Record the door's height, width, material and whether it is insulated, because weight follows material, not width alone.
- Measure the old spring's wire size, inside diameter and length, and note its wind direction or colour code.
- Confirm the measurements against the door's weight, and check shaft, drum and bearing sizes on a torsion door.
- Select a spring that matches all measurements, not just the closest one in stock.
- Fit, wind and balance the spring, and test balance at several heights before the opener is reconnected.
What to check first
Before fitting, check that wire size, inside diameter, length and wind all match the old spring and the door's weight, and that the shaft and drums suit the new spring.
What goes wrong if the problem is delayed
Fitting a wrong-size spring to get a door moving quickly usually means a second visit: the door will not balance, the opener will strain, and the spring will need replacing again with the correct size.
What this guide is, and is not
Included: This guide covers measurement and sizing only. It is not a repair quote, and it does not teach winding or tensioning.
Not included: No price or arrival time is stated on the How to Measure and Size a Spring page, because neither has been supplied for this business. No DIY winding tutorial is published on this site, for safety reasons explained in the safety guide.
Questions readers ask
Can I measure my own spring and order one myself?
Measuring a spring under tension is dangerous and should not be attempted at home. The measurements in this guide explain what a technician measures and why, so a replacement can be judged, not so a homeowner can wind a spring safely.
Why does my door need a different spring from my neighbour's identical-looking door?
Doors that look alike can weigh very differently: insulated steel, uninsulated steel, wood and wood-look doors all carry different weights, and the spring is sized to weight, not appearance.
What happens if a spring is slightly too strong or too weak?
A too-strong spring lifts the door on its own and can pull it upward unexpectedly, while a too-weak spring leaves the door heavy and strains the opener. Both are balance failures, and both wear other parts until corrected.
Call for help with this problem
Call (877) 318-0816 for help with how to measure and size a spring.
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