A number of X-ray instruments have been active in observing the solar coronal X-ray radiation this decade. We have compared XSM observations with simultaneous GOES and RHESSI observations. We present flux calibrations for all instruments and compare XSM and GOES total emission measures (TEM) and temperatures ( T). The model-independent flux comparison with XSM and GOES data in the 1 - 8 Å band shows that the fluxes agree with a ratio of 0.94±0.09 for the data up to April 2005. The Mewe model-dependent Ts and TEMs differ as XSM observes 1.47±0.03 times higher Ts than GOES and 1.23±0.08 times higher TEMs and 0.92±0.05 times lower fluxes. The comparison with RHESSI data in the 6 - 8 keV band shows that the average XSM/RHESSI flux ratio is 2.63±0.23. The discrepancies revealed in this study are similar to discrepancies observed in a number of other spaceborne cross-calibration studies.