A method and system are provided to determine fill sufficiency of a biosensor test chamber by determining capacitance of the test chamber in which an electrochemical reaction is initiated in the test chamber and an oscillating voltage of a predetermined frequency is applied to the chamber. A phase angle between a current output and the oscillating voltage from the chamber is determined and the capacitance is calculated based on a product of the current output and a sine of the phase angle divided by a product of two times pi times the frequency and the voltage.