Spectrometry in radiation fields generated by high power lasers is challenging, since the radiation is created in ultra short pulses (10-14–10-12 s) and thus standard spectrometric methods cannot be applied. The electromagnetic calorimeter developed within this study is an active system that can be used for such spectrometry in the energy range from tens of keV to tens of MeV; even for high repetition rate petawatt class laser systems (10 Hz). The calorimeter comprises of a set of scintillators that are wrapped in PTFE and placed into a 3D printed holder. Scintillation light is detected by a CMOS camera, the acquired dose-depth curve is then evaluated by a dedicated unfolding algorithm. In this paper, the calibration of the calorimeter using Cs-137 and Co-60 radioactive sources is presented. The results demonstrate the developed calorimeter is able to determine energy of impinging radiation with an uncertainty of approximately 10%.