Introduction. Electrocardiographic imaging (ECGI) can characterise car-diac pathologies such as atrial fibrillation (AF) through specific markers based on frequency or phase analysis. In this study, the effect of the geome-try of patients’ torso and atria in the ECGI resolution is studied. Methods. A realistic 3D atrial geometry was located on 30 real patient tor-sos and ECGI signals were calculated for 30 different mathematical AF sim-ulations in each torso. Dominant frequency (DF) and reentrant activity anal-ysis were calculated for each scenario. Anatomical and geometrical meas-urements of each torso (30-80% of variability between patients) and atria were calculated and compared with the errors in the ECGI estimation versus the departing EGM maps. Results. Results show evidences that big chest dimensions worsen the non-invasive calculation of AF markers (p<0.05). Also, higher number of visible electrodes from each atrial region improves ECGI characterization measured as lower DF deviations (0.64±0.26 Hz vs 0.72±0.27 Hz, p<0.05) and higher reentrant activity coincidence (10.1±12.2% vs 3.4±3.4%, p<0.05). Conclusion. Torso and atrial geometry affect the quality of the non-invasive reconstruction of AF markers such as DF or reentrant activity. Knowing the geometrical parameters that worsen non-invasive AF maps may help to measure each detected AF driver reliability.