Spring Rate Calculator
Copyright © 2003 Eric Fahlgren
Last updated 2007-09-18 11:09 PDT

Calculator

Compute a coil spring's rate given its material properties and dimensions.

Parameters
Young's Moduluspsi
Poisson Ratio 
Wire Diameterin
Coil Diameterin
Free coils 
Shear moduluspsi
Spring ratelb/in
 

Notes

A spring's rate is extremely sensitive to its wire diameter, since rate is proportional to wireDiameter4. Try modifying the diameter by 0.010" and see what happens. If you expect to get good results from this calculator, you must measure your springs very accurately.

Count the number of coils starting at one end of the spring as it touches the perch, then count coils along its longitudinal axis. You can have fractional counts, so estimate how much of a turn the spring has left at the last coil above the other perch. The example to the left has 4.5 coils.

 
 
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