 Matter density parameter

The matter density parameter is the ratio of total nonrelativistic matter density, including baryonic and dark matter, to the critical density ${\rho }_{\mathrm{crit}}=3H^2/(8\pi G)$ at the same epoch. A present-epoch value uses $H_0$ and ${\rho }_{m,0}$. It is not the total cosmological density parameter when radiation or vacuum energy also contributes.