The consistency of physics constraints imposed on a core plasma in a tokamak reactor is investigated. Conditions for the steady-state operation of the International Thermonuclear Experimental Reactor (ITER)-grade plasma are listed, i.e., the density limit, the critical beta, feasibility of full current-drive and divertor functions, etc. The parameter regime, in which these guidelines are simultaneously satisfied, is investigated. Based on the available data base, the consistency of the conditions is examined. The L-mode scaling of the energy confinement time is employed for extrapolation to the ITER-grade plasma. The Q value and the size dependence are studied. The consistent operating regime of the steady-state operation is found. If off set-linear scaling is applied, the minimum and necessary input power is ∼130 MW, which enables the full current drive and the steady-state operation of Q = 2.3 with Ip = 20 MA. When the input power is increased to 200 MW, a Q value of 5 is predicted.