Reduced Planck units ($\hslash =c=8\pi G=1,M_{\mathrm{Pl}}=1$)

Here the reduced Planck mass $M_{\mathrm{Pl}}=(8\pi G{)}^{-1/2}$ is one, so the Friedmann equation for an energy density $\rho$ is $3H^2=\rho$. This differs by a factor of $\sqrt{8\pi }$ from setting the ordinary Planck mass to one; the convention must be stated in inflationary amplitudes.