A method and apparatus for monitoring the delivery of a solid precursor from a vessel to a process chamber via a process gas produced by flowing a carrier gas into the vessel is provided. The precursor typically changes state from a solid to a gas (vapor) through a sublimation process within the chamber. The apparatus comprises a gas analyzer to generate a first signal indicative of a density of the precursor in the process gas and a controller. The controller receives the first signal and a second signal indicative of a volume flow rate of the process gas or the carrier gas and calculates a mass flow rate and/or a total amount consumed of the precursor based on the first and second signals. The controller may calculate an amount precursor remaining in the vessel based on the total amount consumed and an initial amount. The amount of precursor remaining in the vessel may be used by an operator to efficiently schedule replacement or replenishment of the precursor in an effort to minimize material waste and processing down time.