This paper proposes an analytical computation of the rms current flowing in the input DC capacitor of a PWM inverter. For a chosen PWM control, switching angles are computed in order to estimate the spectrum of the input current, which is the key design parameter of the input capacitor. The calculation takes into account the AC current ripple, as it can be important, especially for interleaved inverters. The impact of the neutral connection between AC and DC side is also studied. The spectral repartition of the current in the DC capacitor is shown and compared to simulation results. The impact of the AC current ripple, of the PWM generation and of the number of interleaved level is discussed.