Spring calculator

Choose millimetres and newtons or inches and pounds-force, then a spring type. Dimensions are the wire diameter and the outside diameter (what you measure with calipers); the mean diameter D is OD − d.

Compression — rate k = G·d⁴ / (8·D³·Na). Pick the end type (it sets total coils and solid length) and seating (for buckling). Enter up to two working loads to see deflection, length, shear stress τ = K_w·8FD/(πd³), and the safety factor against the allowable stress. Checks: spring index (4–12), solid safety (can it be closed fully without taking a set?), travel, and buckling (free length over 2.63·D/α). Enter a target rate to solve for the active coils.
Extension — the rate uses body coils plus G/E for the hooks; loads below the initial tension do not open the coils. The preferred initial-tension range for the index is shown, and hook bending stress (where extension springs usually break) is checked as well as the body.
Torsion — rate per turn k′ = d⁴E / (10.8·D·Ne), with the legs adding to the effective turns, bending stress with the curvature factor K_i, the deflection for each moment, and the coil’s inside diameter as it winds up so you can check it clears the arbor.

Wire strength follows Sut = A / dᵐ for music wire, hard-drawn, oil-tempered, chrome-vanadium, chrome-silicon, 302 stainless, and phosphor bronze (Shigley’s tables). Allowable stresses are the usual static fractions of Sut (about 45–50% in torsion for steel, 35% for stainless and bronze, 75% in bending for torsion springs).

For static or lightly cycled springs. Fatigue (millions of cycles), surge, and high temperature need a full design — check with the spring maker’s data.

Share link copies a URL that opens this tool exactly as you have it set up. It carries the compression, extension and torsion spring designs. Opening a link replaces your own saved settings for the tool; a Restore my settings button brings them back. To write a link by hand, use units — for example /tools/springs/?units=in.

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