The invention relates to a method (11) for determining a first property (17) of an electrically conductive inner wall (3) of a container (2), wherein the inner wall (3) confines a cavity (4) of the container (2). A standing electromagnetic wave (13) is excited (12) inside the cavity (4), wherein the cavity (4) acts as a cavity resonator. Then, electromagnetic resonance properties (15) of the cavity (4) are measured (14) and the first property (17) of the electrically conductive inner wall (3) is determined (16), based on the measured (14) electromagnetic resonance properties (15). The invention further relates to a container (2) with an electrically conductive inner wall (3) that confines a cavity (4) of the container (2) and an electromagnetic coupling element (8) and/or means for connecting an electromagnetic coupling element (8).