If the speed of light (c), acceleration due to gravity (g) and pressure (P) taken as base units. The dimension of g in the dimensional formula of universal gravitational constant.

 Dimensions of c,

$\left[c\right]=\left[L{T}^{-1}\right]$

$\Rightarrow \left[L\right]=\left[cT\right]$                                         

The dimensions of g, 

$\left[g\right]=\left[L{T}^{-2}\right]=\left[cT T^{-2}\right]$

$\therefore \left[T\right]=\left[c{g}^{-1}\right]$                                                

The dimensions of P ,

 $\left[P\right]=\left[M{L}^{-1}{T}^{-2}\right]=\left[M{\left(cT\right)}^{-1}{\left(c{g}^{-1}\right)}^{-2}\right]$

$=\left[M{c}^{-3}{g}^2{T}^{-1}\right]$

$=\left[M{c}^{-3}{g}^2{\left(c{g}^{-1}\right)}^{-1}\right]$

$=\left[M{c}^{-4}{g}^3\right]$

$\therefore \left[M\right]=\left[P{c}^4{g}^{-3}\right]$

The dimensions of universal gravitational constant.

$\left[G\right]=\left[M^{-1}{L}^3{T}^{-2}\right]$

$={\left[P{c}^4{g}^{-3}\right]}^{-1}{\left[cT\right]}^3{\left[T\right]}^{-2}=\left[P^{-1}{c}^{-4}{g}^3{c}^{3}T\right]$

$=\left[P^{-1}{c}^{-1}{g}^3\left(c{g}^{-1}\right)\right]=\left[P^{-1}{c}^0{g}^2\right]$

Thus, the dimensions of g in the dimensional formula of universal gravitational constant is 2.