I want to use 20amp doblepole breaker to carry 220 v.how many amps they can carry?

Volts Times Amp equal watts
20 X 220 = 4400 Watts, if 240 volts, then 20 X 240 = 4800 Watts, you have to derate to 80% if continuous loads/over 3 hours, so multiply your watts X .8

Well, a 20 amp breaker will carry, hm, I guess 20 amps?

That's the upper design limit.

... ahh... what size wire are you using, or is it in place already?

How does the title "15 amps how many watts" fit into it?