The purpose of this thesis was to research what factors determines the teachers choice in using outdoor educational activities in their mathematics teaching as well as when and where the outdoors mathematics teaching is being used. The research that lies behind the study shows that there is a knowledge gap in the research on outdoor mathematics, since most of the research conducted today is focusing on a more general use of outdoor pedagogical activities irrespective of which subject content it`s applied on. The relevance of the study therefore becomes an important source of knowledge for teachers and students in teaching education. The survey was conveyed by a questionnaire as a research method with the purpose of being able to examine how the use of outdoor mathematics occurs today, in correlation to factors such as professional experience, education or which grade the teacher mostly teaches. The result of the survey showed that many teachers today use outdoor educational activities in their mathematics teaching. The purpose of the use of outdoor mathematics was primarily to vary their teaching and to concretise the subject content. The result also shows that the forest was the place that is best suited for outdoor mathematics according to the teachers. The teachers, however, shed light on the lack of time when planning and implementing lessons, class sizes and human resources as obstacles for outdoor educational activities.