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Engineering tool

Compression spring calculator

Rate k, solid height and Wahl shear stress from wire, outer diameter, free length, coils and end type. Metric units.

Enter a wire diameter greater than 0.

Or enter ID below.

Enter an outer diameter or an inner diameter.

Enter an outer diameter or an inner diameter.

Enter a free length greater than 0.

Enter the total number of coils.

G is a typical published value.

Optional.

Optional.

Results

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Method

Mean diameter D = OD − d (or ID + d). Spring index C = D / d. Active coils: closed or closed-and-ground, Nt − 2; open, Nt; open-and-ground, Nt − 1.

Rate k = G · d⁴ / (8 · D³ · Na) in N/mm. Load F = k · (L0 − L). Shear stress uses the Wahl factor Kw = (4C − 1)/(4C − 4) + 0.615/C.

Solid height is Nt · d when the ends are ground, and (Nt + 1) · d when they are not. G is a typical published shear modulus (SMI / Lee Spring tables), labelled “typical” in the material list. Wire outside Ø 0.40–2.50 mm is flagged because that is our standard range.

Questions

How do you calculate compression spring rate?
k = G · d⁴ / (8 · D³ · Na), with D = OD − d. G is a typical published shear modulus.
What spring index should I aim for?
Keep C = D/d between about 4 and 12. Below 4 the wire is hard to coil; above 12 the coil wanders and the rate is harder to hold.
Why does the tool warn about solid height?
If a working length is at or below solid height, the coils bind and the load shoots up. Change free length, coils or the working position.

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Tell us the spring type, quantity and what it has to do. Our usual minimum order is 5,000–10,000 pcs; smaller development runs are charged.

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