Simple Spring Constant Calculator

This little JavaScript program calculates the spring constant (often denoted as "k") for a regular coil spring. The formulas are from an e-mail Chris L. Johnson posted on the mc-trials list. All input units are inches, to convert mm to inches divide by 25.4

Measure the coil outside diameter and wire diameter as accurately as possible and give number in decimal format.

Spring wire diameter (inches):
Spring outside diameter (inches):
Number of active coils:

Spring constant lb./inch compression
Spring constant kg/mm

The formula used is: k = 11,500,000 X wire diameter to the fourth power / 8 / mean diameter to the third power / number of active coils

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Last modification February 16, 2003
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