Hooke's Law Calculator
Find spring force, spring constant or extension with Hooke's law, plus the energy stored.
About the Hooke's Law Calculator
Choose what to find (force, spring constant or extension) and enter the other two. The calculator also gives the elastic energy stored in the spring.
Hooke's law says the force needed to stretch or compress a spring is proportional to the change in length, F = kx, as long as the spring stays within its elastic limit. The spring constant k measures stiffness: a car suspension spring might be 20,000–50,000 N/m, a ballpoint pen spring about 100 N/m.
The energy stored in the stretched spring is ½kx², which is what launches a catapult or a toy car.
The formula
F = kx; E = ½kx²
Worked example
A spring with k = 500 N/m stretched 0.1 m
- F = 500 × 0.1 = 50 N
- Energy: ½ × 500 × 0.1² = 2.5 J
Questions people ask
What units is k in?
Newtons per metre (N/m).
Does it work for any stretch?
Only up to the elastic limit; beyond it the spring deforms permanently.