Potential difference (V) is defined as work done (W) per unit charge (Q). The dimension of work is $[ML^2T^{-2}]$ and charge is $[AT]$. Therefore, the dimension of potential difference is $[ML^2T^{-2}] / [AT] = [ML^2T^{-3}A^{-1}]$. [cite: 1, 1438]