The robust estimation of the maximum speed of combinatorial elements is of prime importance when comparing different library suppliers or predicting the performance improvement of new processes. Considering the input ramp effect and the input-to-output coupling capacitance, we propose in this paper, a new definition of both the inertial delay and the maximum speed that can be achieved with standard combinatorial gates. Validations are given on several processes ranging from 0.8µm to 0.18µm.