Spring Free Length

Compression Spring & Extension Spring Design Resources – Length

When we refer to Free Length (FL or L), we are describing the overall length of a compression spring or an extension spring. This measurement is taken when there is no load (P) applied to the spring.

On extension springs, engineers will often specify the free length to be the inside hook length rather than the overall length, which is acceptable when properly stated. The following is a simple guide for specifying the free length of an extension spring:

FLOA = Free Length Overall


FLISH = Free Length Inside of the Hooks

Please contact the Newcomb Spring facility nearest you for more information on free length and other considerations of spring design.