When it comes to choosing the right amount of tobacco for your hookah, there are a few factors to consider. The size of your bowl, bowl packing method, and the type of tobacco you use will all play a role in how much tobacco you'll need. Different tobaccos will also burn at different rates, so it's important to experiment to find the perfect ratio for your hookah.
The average bowl can fit 15-20 grams of tobacco, which is the perfect amount for most smokers. Some bowls, however, are meant for solo sessions and can only fit about 12 grams. This is because when smoking alone, you don't need as much tobacco to get a good buzz. A general rule of thumb is that after evenly spreading and leveling the shisha, it has to be approximately two millimeters below the bowl's rim so it would not touch the surface of the foil. This ensures that the heat from the charcoal will be evenly distributed and that your tobacco will be properly cooked.
If you want to learn how to pack a hookah bowl, check this tutorial.