Set up the brew
Measure the vessel's filled working volume rather than relying on its advertised size. A gaiwan labeled 120ml may deliver less once leaf and lid are included.
Method, step by step
Choose a method, weigh leaf, note water volume and record time. For long steeps start near 1g per 100ml; for gongfu begin around 5g per 100ml. Dense ball-rolled or compressed tea needs room to expand.
How to adjust by taste
Increase leaf when the cup has good flavor but lacks body; shorten time if more leaf makes it harsh. Reduce leaf for large casual mugs where the tea remains in contact with water.
Practical guidance
Keep a simple brew log: tea, grams, water volume, temperature, time and one sentence about taste. After three trials you will have a personal ratio, not a borrowed rule.
Identification and caution
Leaf volume by spoon is unreliable because needles, flakes, balls and compressed chunks have very different density. A small scale gives far better repeatability.