Dimensions of momentum

Momentum ($p$) is defined as the product of an object's mass ($m$) and its velocity ($v$).

$$p = m \times v$$

Mass has dimensions of $[M]$ (mass).
Velocity has dimensions of $[L][T]^{-1}$ (length per unit time).
Therefore, the dimensions of momentum are:

$$[p] = [m] \times [v] = [M] \times [L][T]^{-1} = [M][L][T]^{-1}$$

The dimensions of momentum are $[M][L][T]^{-1}$.