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.
Stress at load
Body torsion
––of limit–
Hook bending
––of limit–
Hook torsion
––of limit–
Static loading only.
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k = G * d4 / (8 * D3 * Na), where Na = Nb + G / E. The hooks add a fraction of a coil to the body coils.
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.
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.
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.
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.
Turn your design into real samples.
We prototype custom springs in days, not weeks. Send us your specs to get started.
Get a quoteNot 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.
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Hi there, I am Annie Lin, the key account manager of Zigoal, my team and I would be happy meet you and learn all about your business, requirements & expectations.
Your information will be kept strictly confidential.
Hi there, I am Annie Lin, the key account manager of Zigoal, my team and I would be happy meet you and learn all about your business, requirements & expectations.
Your information will be kept strictly confidential.
Hi there, I am Annie Lin, the key account manager of Zigoal, my team and I would be happy meet you and learn all about your business, requirements & expectations.
Your information will be kept strictly confidential.
Hi there, I am Annie Lin, the key account manager of Zigoal, my team and I would be happy meet you and learn all about your business, requirements & expectations.
Your information will be kept strictly confidential.
Hi there, I am Annie Lin, the key account manager of Zigoal, my team and I would be happy meet you and learn all about your business, requirements & expectations.
