Required spring rate calculator
Find the spring rate your application needs from load and travel. Enter one or two working points and get the required rate in lbf/in and N/mm.
Formula
Use the two-point form when you can measure two loads: it cancels the initial tension of extension springs and any zero offset.
Symbols
Every spring design starts here: you know the force you need and the space you have, and the required rate is one divided by the other.
With two working points (two loads at two lengths) the math becomes immune to extension spring initial tension and reference errors.
With the rate in hand, use the designer to find the wire, diameter and coil count that deliver it with stress margin.
Frequently asked questions
How do I calculate the spring rate I need?
Divide the required force by the available travel: k = F / x. If the spring must exert 11 lbf after compressing 0.4 in, the required rate is 27.5 lbf/in.
What if the application has two loads?
Use k = (F₂ − F₁) / (x₂ − x₁). For example 4.5 lbf at the installed position and 13.5 lbf at full stroke, 0.3 in apart, require k = 30 lbf/in.
How do I turn the rate into a real spring?
Pick a material and an outer diameter that fit the envelope, then adjust wire and coils until the rate matches. The designer runs that search automatically and validates the stress.
Design the spring and get an instant quote
Open the 3D designer, tune the dimensions and see quantity pricing with a technical drawing and stress analysis.
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