Dimension of momentum

The dimension of mass is $M$.

$$[m] = M$$

Velocity is displacement over time, so its dimension is length ($L$) divided by time ($T$).

$$[v] = \frac{L}{T} = LT^{-1}$$

$$[p] = [m] \times [v]$$ $$[p] = M \times LT^{-1}$$ $$[p] = MLT^{-1}$$

The dimension of momentum is $MLT^{-1}$.