Aircraft weight and center of mass are two critical design and operational parameters that have to be within a design envelope to ensure a safe and efficient operation of aircraft. Previous efforts to accurately determine aircraft weight and center of mass before takeoff using landing gear shock strut pressures have failed due to the distortion of measured pressures by shock strut seal friction. Currently, aircraft loading process is controlled with loading sheets and passenger/cargo weight estimation as there are no online measurement systems that can accurately and efficiently estimate aircraft weight and determine the center of mass location before takeoff. However, errors in loading sheets, shifting cargo and errors in weight estimation could lead to incorrect loading of aircraft and, consequently, increase the risk of accidents, particularly in cargo flights. In this paper, an online weight measurement system that can determine an aircraft weight and its center of mass before takeoff is presented. The aircraft weight estimation system is comprised of a few sensing elements, installed on aircraft landing gear shock struts and a weight estimation algorithm that may be executed when aircraft is in motion (forward or backward) while on the ground before takeoff. The algorithm uses mathematical functions to filter sensor measurements and calculate aircraft weight and its center of mass using sensor online readings. A set of data associated with an aircraft flight test is used to simulate the algorithm implementation in offline mode. Simulation results have shown that aircraft weight and center of mass location can be estimated with an acceptable accuracy.