Abstract: With regard to the disadvantages of the conventional iteration method for determining base-plane size of spread footings, a novel analytical method is proposed for design of base-plane size under centric and eccentric loads respectively, according to the concepts of the limit state and the specifications of Chinese National Code of Foundation Design for Buildings. In this method, the check formulae for bearing capacity of spread footings are transformed into cubic and/or quartic inequalities with one unknown quantity, which can be solved easily with Cardan’s or Ferrari’s methodology. For the sake of convenience, the advanced mathematical software such as MAPLE can be used to provide accurate value of base-plane size with a lower limit. Finally, the validity of the proposed method is verified through a case study, which proves the new method can provide good reference for engineering practice.