What size wire to carry 220V about 50 ft?

It depends on the current you wish to carry.

Your relevant electrical code probably has tables both for current limits (to limit heating for fire protection) and for voltage drop. It is usually a good idea to limit voltage drop to 2% or less, which may require a larger wire size than would be dictated by current limits alone. Your code may require a different voltage drop limit. It may also require a different rating for the neutral.

Of course the wire type you choose must be rated for the voltage, temperature, and physical environment (wet, dry, exposed, in conduit, buried) in which you place it.

An AWG12 conductor may be suitable for up to 20A. An AWG6 conductor may be suitable for up to 50A. Your electrical code rules on their suitability.

Most wire you buy in a store is rated for 600 volts. The issue is not the voltage when it comes to household wiring. Current or Amperes is the concern. Find out how much current your going to pull through your wire then I can answer your question. Some quick references. 12awg is good for 20 amps, 10awg is good up to 30 amps, 8 awg is good up to 40 amps, 6awg is good to 60 amps.