Fire performance is one of the main obstacles to an increased use of wood based products in buildings. Fire retardants may considerably improve the fire properties of wood based products. Fire retardant treated (FRT) wood based products can meet even the requirements for Euroclass B, whereas untreated wood products belong typically to Euroclass D. Simple rules for predicting the Euroclass of wood based products on the basis of cone calorimeter data have been developed. These rules can be used in product development of FRT wood based products.