There is no golden rule

there can tell you how much loose tea should be just right when you try to make a good cup of tea.
Tea tasting is highly subjective.
The ways of brewing are utterly influenced by personal preference, tea sets, and tea kinds.
If you want to figure out your own way of brewing catering to your personal tastes, you’ll need multiple tries.

Unlike tea bag

with set amount of tea in it, loose tea can be made either stronger or lighter in taste depending on how you like to brew your tea.
It's important to add the right amount of loose tea to obtain that perfect tea taste.

According to many instructions

given by tea websites and books, 1 gram of loose tea is recommended per 50ml – 60ml cup but this is not always relevant.
You can choose the quantity of tea according to your taste or tea species by adding less or more next time.

Source:  Teavivre