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Spring Constant Calculator

Find a spring constant.

Result

250.00 N/m

How it is calculated

The tool applies Hooke's law, k = F / x. F is the force in newtons and x is how far the spring is stretched or compressed from its rest length, in metres. The result is the spring constant in N/m, shown with two decimals. Because it is a plain ratio, displacement cannot be zero, and the calculation is only valid while the spring stays in its elastic range. A negative force or displacement is accepted, so a compression entered with matching signs still gives a positive k.

Worked example

A 15 N load stretches a spring by 6 cm. Convert the displacement to metres: 6 cm = 0.06 m. Then k = 15 / 0.06 = 250.00 N/m. A 30 N load would stretch the same spring by 30 / 250 = 0.12 m.

Try this example →

Common mistakes

  • Typing the displacement in centimetres or millimetres. It must be metres, otherwise k is wrong by a factor of 100 or 1000.
  • Entering mass in kilograms as force. Multiply the mass by 9.81 to get newtons first.
  • Using the spring's total length instead of the change in length from its rest position.
  • Applying the result to a spring loaded beyond its elastic limit, where force and extension are no longer proportional.

Sources

About this calculator

This calculator applies Hooke's law, k = F / x, to find a spring's stiffness: the force applied divided by how far the spring stretches or compresses from its resting length. A higher k means a stiffer spring that resists deformation more strongly.

Mechanical and automotive engineers use it to design suspensions, valves and mattresses; physics students use it in lab experiments measuring force versus displacement; and hobbyists use it to match a replacement spring to a project.

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Comments (1)

  • Editorial team

    Hooke's law holds only while the spring stays within its elastic range, so take your load and extension from a small, steady pull rather than a hard stretch. Enter the extension in metres and the force in newtons, otherwise the N/m value is off by a factor of 100 or 1,000. To measure force from hanging mass, multiply kilograms by about 9.81. For better accuracy, test two loads and compare. What spring are you testing?

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