The dimensions of energy per unit volumes are the same as those of :

The dimension of energy per unit volume is equal to the dimension of pressure.

Firstly, the dimension of energy is : $[ML^2T^{−2}]$

The dimension of volume: $[L^3]$

The dimension of pressure : $[L^{-1}M T^{-2}]$

Now, $\dfrac{energy}{volume} = \dfrac{[ML^2T^{−2}]}{[L^3]} = [L^{-1}M T^{-2}]$