Yield-stress fluid flows through porous media are inherent to many industries including filtration, oil & gas and mining and also numerous other applications such as biomedical treatments. These kinds of flows are complicated due to the non-linear rheological behaviour of yield-stress fluids, rendering the conventional Darcy type approach invalid. For instance, a critical pressure gradient must be exceeded to commence the flow of a yield-stress fluid in a porous medium. As the first step in generalising the Darcy law for yield-stress fluids, a universal scale based on the variational formulation of the energy equation is derived for the critical pressure gradient which reduces to purely geometrical feature of the porous media. The presented scaling is then validated by exhaustive numerical simulations using an adaptive finite element method based on the augmented Lagrangian approach and also pore-network simulations. Then other regimes of these kind of flows are studied by incorporating complex rheological behaviour of the yield-stress fluids such as the elastic response and also the sliding nature of soft gels in computational frameworks.