In this paper, we have proposed an analytical model for optical networks with full wavelength conversion at the nodes. We have derived an analytical expression to compute the carried traffic on links of the network for fixed routing with uniform traffic distribution (UTD). The carried traffic on a link in the network is thinned proportionately based on the blocking probability of the other links on the route. The blocking probability of the network is estimated using Erlang fixed point approximation with the reduced load on the links. The channel utilisation at a particular load is derived using the blocking probability. Thus the analytical model gives an estimate of the blocking probability and the channel utilisation at any given load and is applicable to any network topology. We have computed the carried traffic for a few example networks, such as 14 node NSFNET, 20 node ARPANET and 20 node INDIANET and validated the analytical results with simulations. We show that the analytical method performs well in the desired range of blocking probabilities and it is computationally efficient. © 2007 IEEE.