In this paper, we present a fast, segment-based approach to estimate the functional coupled-noise value at the receiver pins of a net with minimal loss of accuracy. The net is suitably modeled into segments consisting of two-pi, three-pi or four-pi models. The noise contribution due to each segment on a receiver pin is then calculated. The average error of our model was less than 8% when compared with a spice-like simulator while requiring an order of magnitude less run time. This is the first work in our knowledge to use a segment-based approach for fast noise estimation that is reasonably accurate while taking into account the noise contribution at a sink pin due to coupling noise at the branches. We show that the noise on a receiver pin due to coupling nets coupled to the branches can be of the same magnitude as the noise contribution of coupling nets not coupled to the branches, and therefore cannot be ignored.