I am shopping for a spring on McMaster and there is a quantity listed as "rate constant". Is this the same thing as spring constant? If so, what are the units of this value? (lbs/in, lbs/ft, other)?

  • $\begingroup$ Dn’t you choose the units as part of the selection process on that site? $\endgroup$
    – Solar Mike
    Jan 7, 2018 at 17:46

1 Answer 1


Spring rate can be specified either for a whole spring or per unit length which is often more convenient if you are buying spring stock to cut to length.

The constant of a whole spring is force per unit length of extension the rate constant will be F/L/L so force. This isn't particularly physically meaningful but is convenient if you are buying spring stock in bulk lengths.

So say you buy spring stock with a rate constant of 106 lb then if you make a 6" spring form that then the spring constant for that spring is 106lb/6" ie 17.66lb/inch ie it exerts a return force of 17.7 pounds for every inch it is compressed.


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