This paper presents a closed-form and non-iterative solution for the long-studied SCADA-based State Etimation (SE) problem, where unsynchronized traditional measurements from Remote Terminal Units (RTUs) are used. In this regard, a novel reformulation of the problem is introduced where unknowns are expressed as complex variables in terms of unsynchronized SCADA measurements. To this end, it is assumed that bus voltage amplitudes as well as current amplitudes and active and reactive power flows/injections are available. The resulting system of equations is solved by the classic linear weighted leastsquares method. In contrast to the traditional approaches, several drawbacks such as initialization and issues with convergence (especially for large-scale systems) are resolved. Moreover, the proposed approach does not use synchrophasors. The method is validated on a 3-bus test network and applied to the IEEE 118-bus test system, 1341-bus and 9241-bus European high-voltage transmission networks.