Poissons Ratio Calculator

What Is Poisson Ratio?

Poisson ratio describes how a material expands or contracts laterally when stretched or compressed along one axis. Rubber shows large lateral expansion under tension, while cork barely changes width when compressed. Most engineering metals have Poisson ratios between 0.25 and 0.35.

Calculation Methods

From strain measurements, Poisson ratio is the negative ratio of lateral strain to axial strain:

$$\nu = -\frac{\varepsilon_{\text{lateral}}}{\varepsilon_{\text{axial}}}$$

For isotropic, homogeneous materials, Poisson ratio can also be found from elastic moduli:

$$\nu = \frac{E}{2G} - 1$$

where $E$ is Young modulus and $G$ is shear modulus. Both moduli must use the same pressure units, such as gigapascals.

Frequently Asked Questions

What is a typical Poisson ratio for steel?

Most steels have a Poisson ratio near 0.30. With Young modulus around 210 GPa and shear modulus around 80 GPa, the formula gives approximately 0.30.

Can Poisson ratio be negative?

Most common materials have positive Poisson ratios between 0 and 0.5. Auxetic materials can have negative ratios, but they are uncommon in everyday engineering.

What does a ratio of 0.5 mean?

A value of 0.5 corresponds to a perfectly incompressible material that maintains constant volume under deformation, such as rubber near room temperature.

When should I use strain vs modulus method?

Use strain when you have tensile or compression test data. Use the modulus formula when you know Young and shear moduli from material property tables for isotropic materials.

What is lateral strain?

Lateral (transverse) strain is the relative change in width or diameter perpendicular to the applied load direction. It is compared against axial strain along the load direction.

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What Is Poisson Ratio?

Calculation Methods

Frequently Asked Questions

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