Free extension spring calculator from Zigoal. Enter your spring specs to get spring rate, initial tension, hook stress and maximum load instantly, in metric or imperial units.
Zigoal Extension Spring Calculator
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Results
- –
Stress at load
Body torsion
––of limit–
Hook bending
––of limit–
Hook torsion
––of limit–
- Under 75%
- 75 to 100%
- 100 to 125%
- Over 125%
Spring details
Static loading only.
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Frequently asked questions
How is spring rate calculated?
k = G * d4 / (8 * D3 * Na), where Na = Nb + G / E. The hooks add a fraction of a coil to the body coils.
What is initial tension?
Extension springs are wound with the coils pressed together. Fi is the load that starts to separate them. Below Fi the spring does not extend. Above it, F = Fi + k * y.
Which spring index is best?
Keep C = D / d between 4 and 12. Below 4 the wire is hard to coil. Above 12 the rate and the initial tension are hard to hold within tolerance.
What do the stress lights mean?
Each light compares a stress with its static limit, a share of tensile strength from Shigley, Table 10-7. Under 75% of the limit is comfortable. Up to 100% is within it. Above 100% is overstressed.
Why do hooks fail first?
The bend where the hook meets the body concentrates stress. Hook bending or hook torsion usually reaches its limit before the body does. A larger bend radius lowers it.
Still have questions about your spring?
Send us your specs and our engineers will review them and send back a quote.
Contact our engineersNot sure how to measure your spring? Read our guide on how to measure an extension spring.
Working on a different spring type? See all Zigoal spring calculators, or learn more about our custom extension springs.
