Spring Constant Calculator
Spring constant k = F ÷ x by Hooke’s law, or force or stretch from the other two, with stored energy. Force in N, kN, lbf or kgf; k in N/m, kN/m or lbf/in. How it works
Use the Spring Constant Calculator
About the Spring Constant Calculator
A spring that stretches 0.2 m under 50 N has a spring constant of 250 N/m, from Hooke’s law k = F ÷ x, and it stores 5 J. This spring constant calculator also solves for force (F = k × x) or displacement (x = F ÷ k), in N, kN, lbf or kgf and m, cm, mm or in.
Hooke’s law worked examples
| Solve for | Known values | Result | In SI units | Stored energy |
|---|---|---|---|---|
| k | 50 N, 0.2 m | 250 N/m | 250 N/m | 5 J |
| k | 10 N, 2 cm | 500 N/m | 500 N/m | 0.1 J |
| k | 4.9 N, 7 cm | 70 N/m | 70 N/m | 0.1715 J |
| k | 1 kgf, 1 cm | 980.665 N/m | 980.665 N/m | 0.0490333 J |
| k | 20 lbf, 1 in | 20 lbf/in | 3502.54 N/m | 1.12985 J |
| k | 50 N, 0.2 m | 1.42754 lbf/in | 250 N/m | 5 J |
| F | 500 N/m, 0.05 m | 25 N | 25 N | 0.625 J |
| F | 200 N/m, 15 cm | 30 N | 30 N | 2.25 J |
| x | 100 N, 2,000 N/m | 5 cm | 0.05 m | 2.5 J |
| x | 50 N, 30 kN/m | 1.66667 mm | 0.00166667 m | 0.0416667 J |
Frequently asked questions
- How do you find the spring constant?
- Divide the force by the stretch: k = F ÷ x. Hang a known weight, measure how far the spring extends from its free length, and divide. 10 N stretching a spring 2 cm gives 500 N/m.
- What units is the spring constant in?
- Newtons per meter in SI. The calculator also gives kN/m and lbf/in: 20 lbf compressing a spring 1 in is 20 lbf/in, which is 3502.54 N/m.
- How much energy does a stretched spring store?
- E = ½ k x², which equals ½ F x. A 250 N/m spring stretched 0.2 m stores ½ × 250 × 0.2² = 5 J; the calculator shows it under every result.
- Is k the same for stretching and compressing?
- For an ideal linear spring, yes. The calculator takes magnitudes, so enter a compression as a positive number; negative values are refused with a message.
- When does Hooke’s law stop working?
- Past the spring’s elastic limit, where it deforms permanently, and for a compression spring once its coils touch. The calculator assumes a linear spring inside that range.
- How do I find the spring constant of springs in series or parallel?
- The calculator takes one spring, so combine the rates first. Side by side (parallel), add them: k = k1 + k2, so two 500 N/m springs make 1,000 N/m. End to end (series), add the reciprocals: 1/k = 1/k1 + 1/k2, so the same two springs make 250 N/m. Then enter the combined k here.
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