I am installing a in-line fan and would like to know the size of wire I should use for a fan 220-240volts, 50 herts, 32 watts, fan speed of 2500 rpm, maximum run of wire of no more than 3-4 meters. Minimum size required.

This link should help you. Electrical Wire Sizes - What Size Electrical Wire Do I Need All we need to know is amps. Watts = volts X amps. Are you sure of the data you gave us?

It would also help to let us know what country you are in. The rules and terms are different everywhere.