What is Poisson's ratio?

Poisson's ratio (ν) is the negative ratio of lateral strain to axial strain when a material is loaded uniaxially. For most engineering materials it ranges from 0 to 0.5. A value of 0.5 means the material is incompressible (e.g. rubber); a value near 0 means very little lateral deformation (e.g. cork).

What units do I enter for strain?

Strain is dimensionless — it is the change in length divided by the original length (ΔL / L). Enter it as a decimal (e.g. 0.003 for 0.3%) or use the % toggle to enter percentage values directly.

Why is Poisson's ratio negative for auxetic materials?

Auxetic materials expand laterally when stretched axially, giving a positive lateral strain for a positive axial strain — so ν becomes negative. This calculator handles negative inputs correctly.

What is the formula used?

ν = −(lateral strain) / (axial strain). Rearranged: lateral strain = −ν × axial strain, or axial strain = −(lateral strain) / ν.

Can I use this for 3D (biaxial or triaxial) stress states?

No — this tool applies only to the uniaxial case (one principal stress direction). For multiaxial generalized Hooke's law, you need the full compliance tensor.

Poisson Ratio Calculator

Name: Poisson Ratio Calculator
Availability: InStock
Author: Nham Vu

Compute Poisson's ratio from strains, or find lateral/axial strain when Poisson's ratio is known.

Calculate

Poisson's ratio (ν) from two strains Lateral strain from ν and axial strain Axial strain from ν and lateral strain

Lateral strain (ε_lat)

dimensionless

Axial strain (ε_ax)

dimensionless

Material presets (fills ν)

Result

Enter values and click Calculate.

Formula Reference

ν = − ε_lat / ε_ax

Where ε_lat is the strain perpendicular to the load and ε_ax is the strain parallel to the load. Both are signed: tensile = positive, compressive = negative.

ε_lat = − ν × ε_ax

ε_ax = − ε_lat / ν

Typical Poisson's Ratios

Material	ν (approx.)
Steel	0.27 – 0.30
Aluminum	0.32 – 0.36
Copper	0.33 – 0.35
Titanium	0.29 – 0.34
Concrete	0.15 – 0.25
Glass	0.18 – 0.30
Rubber	0.45 – 0.50
Cork	~0.00

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Summary

Compute Poisson's ratio from strains, or find lateral/axial strain when Poisson's ratio is known.

How it works

Select the calculation mode: compute Poisson's ratio, find lateral strain, or find axial strain.
Enter the known strain values (dimensionless, e.g. 0.002 for 0.2%).
Click Calculate to get the result instantly.
Use the material presets to autofill typical Poisson's ratio values for common engineering materials.
Review the formula and worked example shown below the result.

Use cases

Verify experimental tensile test results by checking the computed Poisson's ratio against material specs.
Determine lateral contraction of a steel shaft under axial tensile load.
Estimate transverse expansion of a rubber seal compressed axially.
Back-calculate axial strain from known lateral strain in non-destructive testing.
Quick reference for students learning mechanics of materials.
Cross-check finite-element model outputs against analytical expectations.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu