A method and apparatus for calibrating a sensor used to sense the concentration of vaporized hydrogen peroxide (VHP). A concentration of liquid hydrogen peroxide in an aqueous solution is determined and correlated with a corresponding concentration of vaporized hydrogen peroxide indicative of an “actual” vaporized hydrogen peroxide concentration. An error value is determined by comparing the “actual” vaporized hydrogen peroxide concentration to a “measured” vaporized hydrogen peroxide concentration, indicated by the sensor being calibrated. The error value is used to properly calibrate the sensor.