How do you find density in the ideal gas law?

The density is determined by utilizing a variation of the ideal gas law where density and molar mass replace moles and volume.
The original ideal gas law uses the formula $PV=nRT$, the density version of the ideal gas law is $PM=dRT$, where $P$ is pressure measured in atmospheres (atm), $T$ is temperature measured in kelvin (K), $\mathrm{R}$ is the ideal gas law constant 0.0821 $\frac{atm(L)}{\mathrm{mol}(K)}$ just as in the original formula, but M is now the molar mass $\left(\frac{g}{mol}\right)$ and d is the density $\left(\frac{g}{L}\right)$.
By rearranging the formula to $\frac{PM}{RT}=d$ the units of atm, mol and $\mathrm{K}$ will cancel and the value will be left with the $\frac{g}{L}$ units for density.