In construction projects, the quantification of works is a critical, interdisciplinary task often performed through data extraction from design information models of the building or infrastructure. In this context, this works presents the development of an ontology specifically designed to organize information elaborated during Quantity Take-Off operations, with the intent of acting as a reference for both quantification applications and processes. The resulting QTOn ontology is conceived to be interoperable with other construction ontologies such as ifcOWL, DiCOn, etc., ensuring coherence with other project information, promoting standardization of QTO processes and supporting automated quantities extraction from IFC models.