The invention pertains to a mailpiece weight measuring apparatus for use with a high speed automatic mailpiece processing system. The weight measuring apparatus measures the inertial mass of the mailpiece as the weight equivalent. The apparatus includes a device for determining a first velocity of a mailpiece, a device for imparting a force to the mailpiece in a direction co-linear with the first velocity so that the mailpiece exits said force impacting device at a second velocity, a device for determining the second velocity of the mailpiece, a device for determining a change in a parameter proportional to the force imparted on the mailpiece, and a device for determining the weight of the mailpiece based upon the determined first velocity, second velocity and change in the parameter.