This article proposes a practical new method to obtain the moment of inertia of UAV, named ARES. The ARES method simultaneously determined all the elements of UAV's Tensor of Inertia, i.e. the moments and the products of inertia through algebraic solving. The ARES method directly uses the UAV Flight Data to accommodate accuracy issues of modeling such as vehicle's geometrical imperfection; manufacturing defect, any non-symmetrical due component placement, etc. This proposed method was applicable for various purposes of UAV modeling e.g. flight control design, flight dynamics analysis, etc. Conventionally, UAV moments of inertia were estimated by tabulating, CAD-based, or pendulum method. Since these existing methods were constrained by the accuracy and practical issues, we develop the ARES method which using the UAV's flight data to resolve both issues. After undergone appropriate mathematical strategies, the ARES produce a linear construction for algebraic solving technique. The implementation the proposed method in the quadrotor flight data showing that ARES are successfully measured the asymmetrical terms which important for nonlinear controlling, that previously neglected by the conventional methods. Thus, the ARES estimates the UAV Tensor of Inertia in holistic, sophisticated and practical fashion.