The characterization of ion chambers used for dose measurements in radiotherapy varies due to their designs. In addition, the depth dose distributions of the electron beams depend on parameters such as energy, field size, depth, and detector type. It is critical to minimize the variations in these parameters during dose measuremnts in order to deliver the desired dose. However, it is technically challenging to determine the radiation dose of small fields due to the different structures of the detectors used for measuring dose and high dose gradients. The aim of this study was to compare the electron beam parameters and output factor (OF) for different electron fields obtained using three different dosimeters. The energies of the PTW-made Semiflex ion chamber, Roos electron chamber and Farmer ion chamber were compared for small and large fields using Varian-lineer accelerator electron beams. All measurements were performed for 12 MeV, 15 MeV and 18 MeV electron energies. Paired sample t -test was used to compare the groups. Paired sample t -test was used to compare the groups. The electron beams parameters such as R50, Rq, Rp, E0 and EP0 were greater for the Semiflex ionization chamber. The R50 values (mm) of the Roos chamber at 2 × 2 cm2, 3 × 3 cm2 and 4 × 4 cm2 for 12 MeV were 37.62, 43.31 and 47.86 respectively. The same values for the Semiflex chamber were 41.97, 47.33 and 51.05, and the difference between the two ion chambers were 10.36 %, 8.4 % and 6.24 % respectively. The OF for the detectors increased with increasing fields size and electron energy, and showed the largest difference between the Semiflex and Roos ion chambers for the field size of 4 × 4 cm2 at 18 MeV. Thus, Semiflex ion chamber and Farmer ion chamber can be used as an alternative to the Roos ion chamber, which is generally used in clinics.