It is hard to give an exact formula for using dried herbs instead of fresh herbs, as the flavor of both is such a variable factor. With fresh herbs, the flavor depends on how fresh they are and how they have been grown: the soil, climate and time of picking. With dried herbs, it depends on how long and in what conditions they have been kept. Assuming both supplies are fresh and in good condition, allow one teaspoon of dried herbs for each tablespoon of fresh.
In some cases, it is possible to replace one fresh herb with a different, dried one. Dried mint can often be used to replace fresh coriander, for instance, as both herbs marry well with cool, sharp, juicy flavors such as cucumber, garlic, tomatoes and yogurt.