Hello Daniel. The standard rule of thumb in culinary practice for substituting dried herbs in place of fresh herbs is a 3:1 ratio by volume.
In practical measurements, this means for every 1 tablespoon (3 teaspoons) of fresh herbs called for in a recipe, you should use 1 teaspoon of dried herbs. If a recipe calls for 1 teaspoon of fresh herbs, you would use roughly 1/3 teaspoon of dried herbs.
The reason for this difference is that drying removes the water content from the plant cells, which significantly concentrates the essential oils and flavor compounds. Additionally, dried leafy herbs pack more densely into measuring spoons than fresh, leafy sprigs.
There is one small nuance to keep in mind regarding the texture of your dried herbs. If you are using finely ground or powdered herbs rather than whole dried leaves, the flavor is even more concentrated; in that scenario, a 4:1 ratio is safer (about 1/4 teaspoon of powder per 1 tablespoon of fresh). Also, remember to add dried herbs earlier in the cooking process so the heat and moisture can properly rehydrate them and release their aromatics.