An electronic cigarette vaporizer includes a heating element, an air pressure sensor and a microcontroller; the microcontroller stores, processes or determines the extent of each inhalation using signals from the air pressure sensor. The microcontroller can calculate the approximate e-liquid consumption from the extent of each inhalation or provide data that enables an external processor to calculate approximate e-liquid consumption. The extent of an inhalation is a function of one or more of: duration; peak flow rate; average flow rate.