The SI unit of volume is

The S.I unit of volume is ${\text{m}}^{\text{3}}$ (cubic meter)

Because volume of body$=\text{length}\times \text{breadth}\times \text{height}$  

Unit of length or breadth or height in S.I is meter

So$\text{V}=l\text{meter}\times \text{b}\text{meter}\times \text{h}\text{meter}$

$\text{V}=\text{l}\text{b}\text{h}{\text{m}}^{\text{3}}$