The soil water content affects rates of oxygen diffusion and redox potentials (E_H). When water‐saturated soils become aerated, a switch from reducing to oxidizing conditions occurs. However, limited information is available at which air‐filled pore volume ε this shift happens. To obtain values of ε, undisturbed soil cores were taken from a Fluvisol and a Gleysol that differed in structure and clay content. Experiments on submergence and drying following a new experimental design were performed in the laboratory. After submergence, the cores were sealed with a glass hood to exclude oxygen and to achieve reducing conditions (E_H < –100 mV). We then aerated the sample by removal of glass plugs in the hood and consecutively measured E_H by platinum (Pt) electrodes and ε by matric potential readings on an hourly basis. From the drying curve we determined two characteristic values: (i) ε_{Pt reaction} indicates the air‐filled pore volume at which a response of the Pt‐electrode from contact with oxygen occurs (i.e. E_H increase > 5 mV hour^–1) and (ii) ε_{Pt aeration} indicates when oxidizing soil conditions are present (i.e. E_H > 300 mV at pH 7). The Fluvisol was characterized by an ε_{Pt reaction} value of 0.036±0.006 cm³ cm^–3 and an ε_Pt aeration value of 0.047±0.005, whereas for the Gleysol these values were 0.048±0.008 and 0.085±0.007 cm³ cm^–3, respectively. We aimed to obtain such characteristic values for different soils to estimate the aeration status of a soil when ε is known, but E_H measurements are unavailable.