Spring Force Calculator

Inputs

Wire diameter (d)

Diameter of the spring wire.

Mean coil diameter (D)

Center-to-center across the coil (outside diameter − wire diameter).

Active coils (Nₐ)

Coils that actually deflect (total coils minus the end coils).

Free length (L₀)

Unloaded overall length — used for solid height and the buckling check.

Deflection (x)

Working compression — used for force and stress at that point.

Material

Sets the shear modulus G and the allowable shear stress.

End type

Sets the inactive end coils and the buckling end-fixity assumption.

Default result

Force at deflection(F)

12.39N

2.786 lbf

At the deflection entered above.

Also computed

Spring rate(k)1.239N/mm

Spring index(C)10

Corrected shear stress(τ)361.2MPa

Within allowable.

Allowable shear stress995MPa

Static limit at this wire size.

Solid height10mm

Buckling (slenderness L₀/D)4

Stable at any deflection.

The load line uses the computed spring rate up to travel-to-solid; the operating marker is clamped at the available travel.

Method notes 3 notes

Static load; ignores fatigue, set and stress relaxation.
Allowable shear stress is the static torsional limit at this wire size (45% of estimated tensile strength), before set removal.
Buckling assumes the ends are seated between parallel flat surfaces.