Is a 30 amp 220 breaker 30 amps on each leg?

A 30 amp double-pole breaker passes the same 30 amps through both legs, because a 240V load is one series circuit. Current flows out one leg, through the load, and back the other; nothing adds.

So it is not 60 amps of capacity. It is 30 amps at 240 volts, which is 7,200 watts, versus 3,600 for the same amps at 120.

The two handles are tied so a fault on either leg opens both, and the breaker occupies two panel spaces to grab both bus phases.

The same logic scales: a 200 amp main is 200 amps at 240 volts total, not 200 per leg summed to 400. Watts, not amp-counting, is how capacity adds.

Size the conductors for any 240V circuit with the 30 amp wire size calculator.