How this calculator works
True strain adds incremental extension relative to the current length, giving the natural logarithm of length ratio. The stress conversion assumes uniform deformation and approximately constant volume. It is useful before necking in a tensile test. After necking, true stress needs the actual local area rather than a global strain conversion.
Formula
epsilon_true = ln(1 + epsilon_engineering); sigma_true = sigma_engineering (1 + epsilon_engineering), for uniform constant-volume deformation.
Worked example
Engineering strain 0.25 gives true strain ln(1.25) = 0.22314355. Engineering stress 80 MPa then corresponds to true stress 100 MPa under the uniform-volume assumption.
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Frequently asked questions
Which logarithm is used?
Use the natural logarithm, not base ten.
Can engineering strain reach -1?
No. That would mean zero final length, so its logarithm is undefined.
Can I convert stress after necking?
The simple conversion is no longer adequate once the cross-section deforms non-uniformly.