Spring constant calculator (Hooke's law)
Hang a known weight or push with a known force, measure the displacement, then enter both values. Suits physics labs and spring selection.
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How to use it
- Enter force and extension or compression.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Hooke's law F = k x, so k = F ÷ x. Stored energy E = ½ k x².
Example
Inputs: Force = 50 N, Extension or compression = 10 mm. Result: Spring constant: 5,000 N/m; Spring constant in N/mm: 5 N/mm; Stored energy: 0.25 J.
Limits and caveats
- Hooke's law holds only within the elastic limit; beyond it the spring will not return to its length.
- Assumes a linear spring; some conical or variable-pitch springs are not.
Questions about this tool
How do I turn a weight in grams into force?
Multiply the mass in kg by 9.80665, so 500 g gives about 4.903 N.
What if I join two springs?
In series: 1/k = 1/k₁ + 1/k₂. In parallel: k = k₁ + k₂.
Is 1 N/mm the same as 1000 N/m?
Yes. A metre is 1000 mm, which is why both values are shown.