Spring Design Calculator

Inputs

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Required spring force at the working deflection.
N
Travel from free length to the working load point.
mm
Mean coil diameter. Outside diameter will be D + wire diameter.
mm
Spring index C = D/d. Values around 6-10 are a common starting point.
Unloaded spring length used for solid-height and travel checks.
mm
Increment used to make a shop-plausible rounded wire candidate. Replace with your supplier wire-size increment when known.
mm
Increment used to round active coils for a candidate design. Many first-pass layouts use whole or half active coils before supplier review.
coils
Sets shear modulus and allowable stress.
Sets inactive end coils and solid height.

Results

Default result
Edit inputs
Wire diameter(d)
2.5mm
Pass

Also computed

Active coils(Na)Pass9.68

Approx. total coils(Nt)11.68

Spring rate(k)5N/mm

Corrected shear stress(tau)Pass193MPa

Below allowable static stress.

Allowable shear stress871.2MPa

Spring index(C)8

Method notes 3 notes
  • This is a first-pass geometry design. It chooses wire diameter from your target spring index, then solves active coils from the rate equation.
  • The rounded candidate uses your wire and active-coil increments so the exact answer is immediately checked against a shop-plausible design.
  • Fatigue, set removal, surge frequency, tolerances and end grinding allowance are not modeled.

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