I.Pellmann für die COSY-11-Kollaboration, Institut für Kernphysik, Forschungszentrum Jülich D-52425 Jülich
COSY-11 is an internal experiment at the Cooler Synchrotron and storage ring COSY at the Forschungszentrum Jülich. Luminosity determination is performed in different ways at the same time together with the reaction under investigation. The calculation from target thickness, number of particles in the COSY-beam, and overlap of both is suitable for a first estimate. Comparing the beam lifetime with and without target allows a luminosity determination as well since it depends at given emittance on both the vacuum pressure of the COSY and the target thickness. Two further methods are based on measurements of reactions with a known cross section. In our case the elastic pp scattering and the reaction pp->d pi+ can be used. Especially, the elastic scattering is well suited because of its well known and high cross section. Realisation of the different methods and their precision will be presented.