How many amps can 12 AWG handle?

Twelve AWG copper is limited to a 20 amp breaker for ordinary circuits. That is NEC 240.4(D), the small-conductor rule, and it is why 12 gauge and 20 amps go together in every house.

The wire's raw ampacity is higher, 25 amps at 75C, which explains the confusion. The code holds small conductors below their table number as a safety margin for the way homes actually load them.

So no, 12 AWG cannot take 30, 50, or 60 amps on a standard breaker. Exceptions exist for specific equipment like air conditioners and motors, where the breaker may be larger while the wire stays protected by the overload device.

Aluminum 12 AWG is rated lower still, 15 amps.

The 12 gauge amperage calculator shows the breaker limit and the exceptions, with the code article cited.