What is Dimensional Formula of Poisson’s ratio?

Poisson’s Ratio is defined as the ratio of lateral contraction to linear elongation . It can also be defined as the ratio of unit transverse (Lateral) strain to unit longitudinal strain.

Mathematically,
Poisson’s ratio (σ) = Lateral Strain / longitudinal strain.

Since we have different form of strain in the above equation and Dimensional Formula of Strain = M⁰L⁰T⁰.

And we know that ratio of dimensionless quantity is Dimensionless.

Therefore, Poisson’s ratio is Dimensionless and has no SI unit.