### Extension Spring Rate Constant Calculator and Formula

This spring rate constant calculator will determine any of the values remaining by changing one of the variables then select 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.

Equation: *k = Gd ^{4}/8nD^{3}*

Where:

k = Spirng 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

*This calculator requires a java - enabled browser*)

Open **Extension Spring Rate "k" Constant Calculator**

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