True Strain vs. Engineering Strain
Engineering strain measures deformation relative to the original length: ε = (L − L0)/L0. True strain instead accounts for the continuously changing instantaneous length during deformation, giving εt = ln(L/L0).
At small deformations, the two are nearly identical, but they diverge at larger strains — true strain is the more physically accurate measure for large plastic deformation, such as in metal forming, and is additive across successive deformation steps in a way engineering strain is not.
Last reviewed August 2026