A numerical model that simulates ice accretion amounts and ice shapes on wind turbine blades is presented. The model simulates both rime icing due to fog droplets and glaze icing due to precipitation at all angles of droplet attack experienced by wind turbine blades. Icing can be simulated by the model also when the blade is heated. The sensitivity of ice accretions to meteorological variables is studied and predictions of the model are compared to data from icing wind tunnel experiments and from a field study of natural wind turbine icing. Applications of the model in the design of blade heating elements for anti-icing of wind turbines are described.