Boss-S2K

How much paint would I need to repaint my car? It's currently Berlina Black, I'm going to sand off the existing clear and have more coats of black put over my current one as there are some defects. Will one gallon be enough? With reducer would be two gallons right? Will a gallon of clear coat be enough too? Most likely will be using PPG's high grade paint, not the economy one.
Thanks!