Contemporary Full Hybrid Electric Vehicle/Plug-in Hybrid Electric Vehicle/Battery Electric Vehicle (FHEV/PHEV/BEV) products use one or more DC/AC power converters, also known as traction inverters, to convert the DC voltage/current provided by the traction battery to the AC voltage/current to drive the traction motor(s). Large and bulky DC link capacitors are used at the input of the traction inverter to provide a smooth DC input voltage. Those DC link capacitors, occupying almost 50% of the space in the whole package, can contribute to more than 20% of the total cost of the traction inverter. They are generally over designed to assure a large safety margin during the fast transient operation of the electric machine(s). However, it is not well understood how the capacitor size reduction affects the electric machine drive system performance and operation stability. This work presents the numerical method of calculating the DC link capacitor current ripple of the traction converter for electric vehicle applications. The effect of internal resistance of the input voltage source is taken into account for the math modeling. This provides guidance to the minimum boundary of the DC link capacitor size of traction power inverters for the application of battery electric vehicles.