This extension spring calculator estimates the wire length from the mean coil diameter, the number of coils, and an allowance for the two end hooks. Enter the values above.
Formula (approximate)
Wire length ≈ π × D × N + hook allowance
Example
D = 0.75 in, N = 20, hooks 3 in: length ≈ π × 0.75 × 20 + 3 = 50.1 in.
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Frequently Asked Questions
How do I calculate extension spring wire length?
Multiply pi by the coil diameter and the number of coils, then add an allowance for the two end hooks.
Why add a hook allowance?
Extension springs have loops or hooks at each end that use extra wire beyond the coiled body.
Are extension springs close-wound?
Usually yes. The coils touch at rest, which the pi times D times N estimate assumes.