Systems and methods of supplying marking fluid in an imaging system are described. In one aspect, height signals indicative of relative marking fluid levels in a marking fluid tank reservoir are generated. A measure of marking fluid flow rate is computed based upon multiple height signals generated during at least a portion of a startup period extending from a time when flow of marking fluid to the imaging assembly is insubstantial to a time when marking fluid in the marking fluid tank reservoir reaches a substantially steady-state level.