This work presents an investigation for process capability in additive manufacturing (AM). Fused Filament Fabrication (FFF) is the additive manufacturing method, which is based for this verification. The typically layer-upon-layer building method in FFF has special effects to the geometrical quality and is important for comprehending the challenges in the additive manufacturing. But the continuously increasing of manufacturing quality in AM methods has enlarges the applying from rapid prototyping to rapid manufacturing or even to rapid tooling. The reliable applying of AM methods in these areas needs an evaluation and validation for process stability and is part of this paper. The necessary tolerance specification for purposing the process capability is common in mechanical engineering and is considered in results.