Spring Rate Calculator

Spring rate (or spring constant) is the amount of force needed to compress or extend a spring by a given distance, and it's the key figure for predicting how a compression or extension spring will behave under load before you have a physical sample to test. This calculator works out the rate of a helical coil spring from its outside diameter, inside diameter (or wire diameter), and number of active coils, along with the material's shear modulus.

For a conical disc (Belleville) spring instead of a helical coil spring, see our Belleville or Disc Spring Calculator.

Enter your values and select SOLVE. CLEAR ALL will clear all fields.

RELATED PAGES

• Belleville or Disc Spring Calculator
• Material Strength
• Metal Properties

FREQUENTLY ASKED QUESTIONS

What's the difference between "active coils" and the total number of coils?

Active coils are the coils that actually contribute to the spring's flexing behaviour; a compression spring's end coils are often ground flat or closed up to provide a stable seating surface and don't flex under load, so they're excluded from the active coil count used in rate calculations.

Does wire diameter have a big effect on spring rate?

Yes, a very large one — spring rate is proportional to the wire diameter raised to the fourth power, so even a small change in wire diameter has a dramatic effect on stiffness compared to changing the coil diameter or number of coils.

Why does my calculated rate not match a spring I've measured?

Manufacturing tolerances, end coil grinding, material variation, and whether the spring is operating within its linear range can all cause a measured rate to differ slightly from a theoretical calculation — treat the calculated value as a close design estimate rather than an exact guarantee for a specific manufactured spring.