Annual and sub-annual tree-ring 14C measurements allow the study of past natural phenomena such as rapid 14C increases and solar behavior. In addition, they provide precise calibration data sets that help in improving the dating accuracy of past natural and cultural events. However, for the data to be comparable, it is important that laboratories describe the whole process from sample retrieval to eventual results. In this paper, we describe the full 14C measurement procedure adopted in the Finnish tree-ring consortium, including sample collection and preparation, dendrochronology, chemical pretreatment, combustion and graphitization, Accelerator Mass Spectrometry (AMS) measurements and data processing. In addition, we report the 14C background components for our traditional Closed-Tube Combustion (CTC) and Elemental Analyzer (EA) based processes, both yielding to high-quality data. Furthermore, we study the mass-dependence effects of tree-ring measurements and find them to be practically insignificant for ages up to several millennia but growing in significance when approaching the 14C limit.