Spring Constant (k) Calculator and Formula

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Extension Spring "k" Constant Calculator and Formula

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This Popup calculator will determine any of the values remaining by changing one of the variables then selecting the "calculate: button for the selected variable.

This calculator will calculate (estimate) the Spring Rate (k) of a extension spring. Spring rate is best determined by test and measurement techniques.

k = constant, pounds of load per inch of deflection

G = modulus of rigidity of spring material, pounds per square inch

d = wire diameter, inches

n = number of active coils, which is the number of coils subjected to flexure (always less than the total number of coils)

D = mean coil diameter, inches = Outer Diameter - Wire Diameter

Equation: k = Gd⁴/8nD³

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