We report on a new method to calibrate the FORMOSAT-7/COSMIC-2 (F7/C2) ion velocity meter (IVM) in-situ ion density data using the Tri GNSS (Global Navigation Satellite System) Radio-occultation System (TGRS) differential total electron content (TEC) data. This calibration is made using collocated measurements from the IVM and TGRS instruments on the same satellite. We found that the IVM ion density is about 8-15% lower than the TGRS derived density at the insertion orbit (~ 710 km) and 5% higher at the mission operation orbit (~ 540 km). Using a linear correction specific to orbit altitude and satellite, an adjustment is implemented for the IVM density data. These corrections remove the offsets between the IVM and TGRS density measurements. We believe the corrected densities eliminate any inter-spacecraft discrepancy in the IVM density data, making it suitable for use in multi-satellite scientific investigations of longitudinal and local time variations and space weather operational applications.