When all else fails, go to "Joy of Cooking" --see "equivalents and or substitutions, and I quote:
1 Tsp raw ginger = 1/8 tsp pwd. This info is usually on the spice container, but I
use a less expensive brand and it does not have the info. cmg
Avoid doing this. The proportions unbalance a recipe when you substitute ground for freshly grated ginger.
It is a spice
A one inch piece of fresh, grated ginger (generally yielding 1 tablespoon) equals approximately 1/8 teaspoon ground (dried) ginger. Source: http://www.evitamins.com/healthnotes.asp?ContentID=3602003
1 inch of ginger grated will produce about 4 teaspoons.
Forty grams of fresh ginger is approximately equivalent to about 4 to 5 teaspoons, depending on how finely it is minced or grated. Typically, one teaspoon of minced ginger weighs around 8 to 10 grams. Thus, when measuring, it's best to adjust based on your desired texture and flavor intensity.
To substitute fresh ginger with ground ginger in a recipe, use 1/4 teaspoon of ground ginger for every 1 tablespoon of fresh ginger called for in the recipe. Adjust the amount to taste, as ground ginger is more concentrated than fresh ginger.
1 tablespoon fresh rosemary equals 1 teaspoon dried
Dry is always more potent, as long as your spices are not old. If you have "fresh" dry ginger, 1 teaspoon would be the right amount to substitute for 2 tablespoons of fresh ginger. Since ginger is something that loses its potency in dry form very quickly, the best possible answer to this question is "to taste."
No amount of dried ginger equates to any amount of fresh finger; they have two completely different flavors and they will never behave the same in any recipe. Powdered ginger has a deeper, smokier, spicier flavor we know from gingerbread, gingersnap cookies, etc... Fresh ginger is sharp, bright, slightly lemony and even biting. Don't attempt an exchange, no matter what anyone tells you. It won't work.
As a general guideline, you can use 1/4 teaspoon of dried ginger for every 1 tablespoon of fresh ginger in a recipe. Adjust to taste based on your preference for ginger flavor.
Ground ginger can NOT be substituted for crystallized ginger--that is something quite different. Otherwise, you are fairly safe to use ground, minced, and grated ginger interchangeably unless the ginger is being used for garnish purposes (sushi, for instance). The thing to remember is that ground ginger is exponentially more potent than fresh ginger. Ultimately it comes down to a matter of personal taste, but I rarely use more than a few pinches of the ground stuff.
Typically, 1 teaspoon of ginger paste is equivalent to approximately 1/2 inch of fresh ginger. However, this can vary depending on the brand and concentration of the paste. It's always best to refer to the specific instructions on the packaging or adjust to taste when substituting ginger paste for fresh ginger in recipes.