To facilitate comparing applied signs with prior applied or registered signs to determine whether they can be registered as a trademark, an international system is created by means of which groups of products and services with similar characteristics (nature, objective, commercialization and publication channels, consumer, location of sale, etc.) are included in the same International Class.
To establish to what International Class a trademark belongs, the webpage of the International Classification of Products and Service of Madrid can be consulted (see the webpage of WIPO). From International Classes 1 to 34, you can find different product groups; from International Classes 35 to 45, you find different service groups.