The structures of inductive irises are used commonly in waveguide filter, especially at highter frequencyies, due to low loss and high temperature stability. However, the iris thickness can not be neglected, as it could be at the lower frequencies. Approximate models assuming zero thickness fail to predict the exact behavior of the filter. And current thickness correction is introduced which is valid in the case of thick irises only. Account of the effect of round is normally not taken. So the necessity of finding a relation for the two factors-iris thickness and round-arises in the design of waveguide filters. This paper describes a mutual relation that considers the combined effect of finite thickness and round from the start. In order to test the validity of the changed relation, weveral examples are given. And the measured response of each case is then compared with the predicted reponse. And it is shown that the radius is of perceptible influence on the transmission coefficient through a thick iris.