An embodiment of a toner quantity detection device in an electrophotographic printer includes a configuration to determine if sufficient toner is available for performing imaging operations. The electrophotographic imaging device includes a conveyor for moving toner from a first chamber for storing the toner to a second chamber from which a developing roller removes toner for development. A toner concentration sensor measures the concentration of toner in the second chamber. As imaging operations are performed, the toner in the second chamber is depleted. When the toner concentration falls below a threshold level, the conveyor is actuated to move toner from the first chamber to the second chamber, thereby replenishing the toner in the second chamber. Software operating in a computer coupled to the electrophotographic printer estimates an amount of toner required for performing an imaging operation. Between intervals during which the toner in the second chamber is replenished by actuation of the conveyor, the ratio of the change in toner concentration to the estimated amount of toner required is computed. When this ratio rises above a predetermined value, a signal is generated to indicate that sufficient toner to perform imaging operations may not be available.