According to the ideal gas equation $pV = nRT$, the universal gas constant is given by $R = \frac{pV}{nT}$. The SI unit of pressure ($p$) is $\text{N m}^{-2}$ (Pascal), volume ($V$) is $\text{m}^3$, amount of substance ($n$) is $\text{mol}$, and temperature ($T$) is $\text{K}$. Therefore, the SI unit of $R$ is $\frac{\text{N m}^{-2} \times \text{m}^3}{\text{mol K}} = \frac{\text{N m}}{\text{mol K}} = \frac{\text{J}}{\text{mol K}}$ or $\text{Joule K}^{-1} \text{ mol}^{-1}$ .