1.Properties of medicinal herbs
The medicinal herbs moderate in nature can be used in a large amount; those drastic or poisonous in nature must be used in a small amount; those light in property should be used in a small amount; those heavy in property, such as mineral and shell but without toxin can be used in a large amount; fresh plant medicinal herbs, since they contain water, should be used in amount about twice as much as dry ones.

2.Compatibility and dosage
The amount of a singly used herb is usually large than that applied in a prescription; the amount of a main ingredient in a prescription larger than that of an accessory one; the amount of a medicinal herb in making decoction larger than that in pills or powder. For instance, Rougui (Cortex Cinnamomi) used in decoction usually weights 3 g, but if used in pill or powder, it is only needed 0.5 lg.

3.The condition of illness, the patients' physique and age
The amount of a medicinal herb used in the treatment of serious and acute disease must be fairly larger while the amount used in the treatment of the mild or chronic comparatively smaller. The amount used for those with strong physique must be larger while for those with weak physique, the old and children, the dose generally smaller. For children over 6 years, half the dose of an adult's is used; for the children below 5 years, 1/3 - 1/2 dose of an adult's is used; for an infant, the dose should be much smaller.