Ionization gauges have been calibrated by a static expansion method in the pressure range of10−2–10−6Torr with a absolute accuracy of± 3%.The repeatability of the linear calibration curve is 1%. The sensitivity of the gauges thus calibrated has been checked by a dynamic method, comprising a flow measurement through a porous plug and a calculated circular orifice. The accuracy of this method is ± 7%. Evaluation of the measurements of flow and sensitivity is done by an electronic computer. The results agree within the limits of error with those obtained by the static method. The dynamic method can be used for calibrations down to pressures of10−10Torr while the static method has its lower limit at10−6Torr because of sorption phenomena.