How do I know how much water to use?

Just bought one of those already grown basil plants, it’s not fully grown yet. It’s currently the hottest parts of summer where I live so I assume I need to water it quite regularly but I don’t know how much.

Is there a measurement I should use like if there’s x amount soil it needs x amount of water or do I just eyeball it

My understanding so far is basil likes moist soil, not too wet or dry so it is possible I’m under or overwatering

Any help is appreciated