Helical Spring Rate Calculator
Enter shear modulus, wire diameter, mean coil diameter, active coils, and force to calculate rate, deflection, index, and corrected shear.
A QUICK WALKTHROUGH
How to use this tool
- Enter G in MPa, diameters in mm, active coils, and force in N.
- Calculate spring rate, force-based deflection, spring index, and Wahl-corrected shear estimate.
- Review the exclusions before using results in a design.
Equations and units
For round-wire cylindrical compression springs: k = Gd⁴/(8nD³), with G in MPa (N/mm²), d and mean diameter D in mm, and n active coils. Deflection δ = F/k. Spring index C = D/d. Wahl factor Kw = (4C−1)/(4C−4) + 0.615/C; corrected shear τ = Kw × 8FD/(πd³).
Scope limits
This idealized calculation does not assess material allowables, fatigue life, buckling, end conditions, solid height, dynamic surge, manufacturing tolerances, or safety. It does not declare a spring safe or suitable. Formula reference: NASA Technical Report, Spring Design for High Temperature Applications, including spring-rate and Wahl-factor equations: https://ntrs.nasa.gov/api/citations/19700007099/downloads/19700007099.pdf .
GOOD TO KNOW
Common questions
Does this certify a spring?
No. It is an idealized equation estimate, with no allowable stress or safety determination.
Does it cover buckling or fatigue?
No. These and other design checks are outside scope.
Are inputs uploaded?
No. Calculation stays in this browser.