Calculation of cable size

You have to choose the correct cable size when connecting to the mains
when wire size is correct it can cope with the power demands of the device
wire size is in mm2 and this measurement is actually the cross sectional area of the wire inside. The larger that area the higher the current it can carry.
if the amount of current passing through cable were large comparing to cable size it would be very dangerous as the wire overheating and causing a serious safety risk.

use this site to convert and calculate Cable diameter to circle cross-sectional area and vice versa