how do i calculate stall torque 5.4kg@ 5v 1000mA?
It's pretty reasonable to assume they mean kg-cm. The size and form factor of that motor both corroborate this assumption. You can't be sure that is the stall torque, since they did not say that was the stall torque. You also can't determine the stall torque from that number, since stall torque is dependent on the maximum current of the motor. My suspicion is that the stall torque is 2-3x higher than that based on the size of the robot, but that's complete speculation.