Hot spot factors due to fissile material segregation in UO2-PuO2 fuels and to geometrical tolerances in the fuel rods are calculated for both vibrationally compacted and pelleted fuels to produce optimum design for light-water reactors. Neutron flux distribution in the fuel is calculated using the transport theory, while the trend of the heat flux transferred to the coolant is evaluated by a three-dimensional heat-transfer code. Segregation of fissile material is significant for vibrationally compacted fuel, and appears negligible for pelleted fuel. The geometrical tolerances considered give values for engineering hot channel factors that are quite relevant for fuel-rod design.