How to Use the Coil Spring Rate Calculator
Designing a compression coil spring, or checking the performance of one you already have, comes down to a few key dimensions: wire diameter, mean coil diameter, and the number of active coils. This calculator uses those dimensions plus an applied load to compute both the spring rate and the resulting deflection.
The formula is spring rate = shear modulus × wire diameter&sup4; / (8 × mean coil diameter³ × active coils), and deflection is load divided by spring rate. This is the standard shear-modulus-based formula used throughout cylindrical compression spring design. This calculator uses the standard shear modulus for spring steel / music wire, about 11,500,000 psi.
Active coils account for the closed and ground ends common on compression springs, so the number can differ from the total coil count. Real-world design also needs to account for material (spring steel vs. stainless steel have different shear moduli) and fatigue life under repeated loading — for critical components, confirm material-specific properties and finalize the spec with a mechanical design engineer.
Frequently Asked Questions
No. Compression springs often have closed and ground ends, so the active coils that actually contribute to deflection are usually about 1.5-2 coils fewer than the total coil count.
This calculator uses the standard value for music wire/spring steel (about 11,500,000 psi). Stainless steel and other alloys have different shear moduli, so check material-specific properties for precise design work.