Spring Constant Calculator (k = F/x)

k = F / x. Determine spring stiffness from a known force and displacement.

Inputs

Result

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How to use this calculator

  • Apply known force.
  • Measure displacement.
  • Read k.

About this calculator

Spring constant k measures stiffness: how much force per unit displacement. Stiff springs (k = 1000+ N/m): door closers, car suspension. Soft springs (k = 1-50 N/m): toys, foam. Determine experimentally by hanging a known weight and measuring stretch. The relationship F = kx (Hooke's) is a defining property — non-Hookean materials require more complex models.

Frequently asked

How precise is this?+
For ideal springs in elastic region, exact. Real springs may be slightly nonlinear at extremes; linearize around operating point.
Series springs combination?+
Series (end-to-end): 1/k_total = 1/k₁ + 1/k₂. Both stretch — total stretch is sum.
Parallel springs?+
Parallel (side-by-side, supporting same load): k_total = k₁ + k₂. Both share force.
Coil spring k formula?+
k = G × d⁴ / (8 × D³ × N) — G = shear modulus, d = wire dia, D = coil dia, N = active coils. Engineering spec.
Period of mass-spring oscillator?+
T = 2π √(m/k). Independent of amplitude (small oscillations). Used in time-keeping.

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Disclosure of known mold or moisture conditions in a property — required by some states, recommended in all sales/leases.