Orlandi, G.L. Craievich, P. Dehler, M.M. Ischebeck, R. Marcellini, F. Staeger, D. JACoW Publishing Geneva, Switzerland 2673-5350 978-3-95450-230-1 10.18429/JACoW-IBIC2021-WEOB01 English 341-348 FEL cavity electron gun impedance Contribution to a conference proceedings 2021 2021-10 https://doi.org/10.18429/JACoW-IBIC2021-WEOB01 https://jacow.org/ibic2021/papers/weob01.pdf A comparative measurement campaign of the beam charge was carried out at SwissFEL using the following instruments: Faraday-Cup (FC), Wall-Current-Monitor (WCM), Integrating-Current-Transformer (Bergoz Turbo-ICT-2) and the reference cavity of the Beam-Position-Monitor (BPM). The goal of the measurement campaign was to determine an absolute charge measurement method for a general purpose of instrument calibration and machine routine operation. Results of the absolute charge calibration method proposed for SwissFEL will be presented.