Sage is one of the herbs that dries particularly well. However, I wish I knew what dish you’re making, because sometimes I don’t recommend substituting dried sage for fresh. For others, it makes no difference.
For a sage butter sauce for pasta or gnocchi, for example, or for saltimbocca, I wouldn’t substitute dried sage; I’d just wait until I had access to fresh to make the dish. The dried version won’t soften up sufficiently in the cooking, and the texture will be unpleasant. For seasoning pork, pork sausage, duck, or stuffing, dried is fine. Generally, crumbled dried sage is more than acceptable, while powdered sage should be avoided. Any powdered herb rapidly becomes little more than sawdust.
The general rule of thumb is to use 1/3 the amount of dried herb as fresh, but you don’t know what the measure of 6-8 fresh large sage leaves is. Luckily for both of us, I had dried whole sage leaves from last year’s harvest on hand. I sorted out eight of the largest leaves, and crumbled them. The yield was 4 teaspoons. So you can substitute 1 tablespoon to 1 tablespoon plus 1 teaspoon in your recipe. I’d go with the smaller amount, as your recipe probably refers to garden sage.
The variety of sage I grow is Berggarten, which has broader leaves than garden sage. Having grown both, I prefer the Berggarten variety. It’s as flavorful, but the leaves are more tender and perfect for one of my favorite appetizers, stuzzichini di salvia. Tuscans secure an anchovy between two sage leaves with toothpicks, dip it all into a batter and fry in olive oil. Absolutely addictive!