By Zencalcy Editorial TeamLast reviewed About us
Hooke's law says the force a spring exerts is proportional to how far it is stretched or compressed from its natural length, as long as the spring is not deformed permanently. The constant of proportionality, k, measures how stiff the spring is: a higher k needs more force for the same extension.
Spring force, spring constant or extension.
F = k x
F is the restoring force in newtons, k the spring constant in N/m and x the extension or compression in metres. The relation holds only within the spring's elastic limit.
| Symbol | Meaning |
|---|---|
| F | Spring force, in newtons. |
| k | Spring constant, in newtons per metre. |
| x | Extension or compression from natural length, in metres. |
The force is 200 × 0.1 = 20 N. The stored elastic energy is ½kx² = 1 J. Doubling the extension doubles the force but quadruples the energy.
Continue with the Hydraulic Press Calculator, Hydrostatic Pressure Calculator, or the Pressure Calculator — or browse more statics tools and all physics calculators.
A slinky is around 1 N/m, a retractable pen spring around 100 N/m, and a car suspension spring 20,000–40,000 N/m. The value depends on wire diameter, coil count and material.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026