The behaviour of DC corona discharge in air that is free of particulate matter with the wires-to-plane geometry was analysed in this work. The formulae I = KV (V - V0) and I = A (V - V0)m commonly used for the current-voltage characteristics were used to determine the various corona parameters for the two polarities of the corona discharge. Using curve fitting, it has been shown that the geometric factors K and A and the exponent m are strongly affected by the number n of the discharging wires. However, the corona inception voltage determined from the measurements is weakly influenced when n is small, and it remained constant for n > 5 discharging wires. As for the breakdown voltage of the discharge, it is practically independent of the number n. Furthermore, it was verified that the two formulae above can be used for both negative and positive corona in multiple wires-to-plane geometries.