Poisson’s Ratio Calculator
Calculate Poisson’s ratio from signed longitudinal and transverse engineering strains, with ratio, percent and microstrain inputs and model notes.
Calculate the lateral-to-longitudinal deformation ratio for a chosen loading direction. The minus sign in Poisson’s ratio makes ordinary lateral contraction during axial tension positive. Inputs remain signed, allowing an auxetic response to be represented without incorrectly forcing every answer into a positive range.
How to use this tool
- Enter the nonzero longitudinal engineering strain.
- Enter the transverse engineering strain from the same loading state.
- Choose the common strain representation: decimal ratio, percent or microstrain.
- Read the dimensionless ratio and any note about the conventional isotropic range.
Formula
ν = −εtransverse / εlongitudinal
Both strains must use the same reference convention. Extension is positive and shortening negative. A common conversion factor cancels in their ratio, but the selected representation is also used to check the associated dimension changes.
Example
A specimen extends longitudinally by 1,000 µε and contracts transversely by −300 µε. Its ratio is −(−300) / 1,000 = 0.30. If the transverse strain were instead +200 µε, the ratio would be −0.20, indicating same-sign extension in those directions.
Frequently asked questions
Can Poisson’s ratio be negative?
Yes. Auxetic materials can expand laterally when stretched along a particular direction. Keeping the measured signs is essential; replacing strains with absolute values would hide that response.
Must every value be between zero and 0.5?
No. The familiar three-dimensional isotropic elastic range extends from −1 to 0.5, with limiting cases requiring care. Direction-dependent ratios in anisotropic materials need not obey those same bounds. The calculator flags the distinction rather than rejecting every outlying ratio.
Can I enter a zero longitudinal strain?
No. A ratio with zero denominator is undefined. A nonzero longitudinal strain with zero transverse strain gives a ratio of zero.
Is this enough to identify material properties?
A single strain pair does not establish isotropy, linear elasticity or a full constitutive law. Large deformation and different measurement directions can require more detailed definitions. Engineering strains at or below −1 are rejected because they imply a nonpositive final dimension.
Sources
Last updated: 2026-10-30