The performance parameters of a gas cyclone, viz., pressure drop and cut-off diameter, are highly sensitive to its geometry. Cyclone length strongly affects the pressure drop as well as the collection efficiency. The contribution of the present study is therefore twofold. First, the effect of variation in the cylinder as well as the cone lengths on cyclone performance parameters with respect to the standard cyclone model is examined. Second, comparison is presented among the two geometrical variables for similar increase in their lengths. The performance and the velocity field are predicted computationally on ten different test models. It has been found that increasing the cylinder length by up to 5.5 times the cyclone diameter saves about 34% in the pressure loss and enhances the collection efficiency by about 9.5%. On the other hand, increasing the cone length by up to 6.5 times the cyclone diameter shows nearly a 29% reduction in the pressure loss and about an 11% increase in collection efficiency. It is also shown that apart from optimizing the cyclone length, the designed inlet velocity of the cyclone must be considered.