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The ratio is 3:1 - one tablespoon of fresh chopped herb equals one teaspoon of dried. Drying removes the water and concentrates the essential oils roughly threefold. This converter handles the arithmetic in both directions, including ground herbs.
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1 tablespoon fresh (chopped) equals
1 tsp dried (whole leaf)
Dried herbs are about three times as concentrated as fresh, because the water is gone. Add them early so they have heat and moisture to rehydrate in.
These ratios are a rule-of-thumb starting point - potency varies with the herb, its age and the brand, so taste and adjust.
Questions
Three to one. One tablespoon of fresh chopped herb equals one teaspoon of dried. Drying removes the water and concentrates the essential oils roughly threefold, which is where the ratio comes from.
Dried herbs go in early - they need heat, moisture and time to rehydrate and release their oils. Delicate fresh herbs like basil, cilantro, dill, parsley, mint and chives go in at the very end, or they turn grassy and lose their aroma.
Woody herbs like rosemary, thyme, oregano, sage and bay dry well and hold the ratio closely. Soft herbs like basil, parsley and cilantro lose far more of their character in drying, so the dried version is a pale shadow of the fresh one regardless of how much you use.
Ground herbs are roughly twice as strong as dried whole leaf, because grinding exposes far more surface area. They also release everything immediately rather than over time, so add them late and taste as you go.
Per herb