A new method of evaluation of adhesion tension that does not require measurement of the contact angle, which is conventionally used for definition of adhesion tension, is proposed. In this method, adhesion tension can be derived from a function of size and surface tension of sessile drops which are easily, obtained without requiring a high-precision experimental technique for contact angle measurement. In order to derive the function of adhesion tension, potential theory is applied to it with approximating the sessile drop configuration as an ellipsoidal solid. It is confirmed that the method proposed here is appropriate for practical use, since the error of adhesion tension determined with this method is less than 1.5% compared with the solution given by Laplace formula.