Ground ginger and fresh ginger are used very differently in cooking. The ground version of this spice is typically used in baking for spicing up breads and cakes. It's occasionally used as a savoury addition to meats such as chicken or ham and can be an ingredient in spiced drinks such as mulled wine and cider. Fresh ginger is commonly sauteed in Asian-themed dishes or blended to brighten smoothies. Occasionally, the substitution will work, but the two forms should not be considered completely interchangeable.
Measure out 1/8 tsp of ground ginger for 1 tbsp of fresh ginger. This may seem like a large difference, since 1/8 tsp is barely a few shakes, but ground ginger is quite potent and a little goes a long way.
Cook with ground ginger more cautiously than you would with fresh. Add it to the beginning stages of a sautee or a curry sauce to allow the flavours to mellow and permeate the dish. Because ground ginger doesn't have the zesty, bright appeal of fresh ginger, it's best not to sprinkle it on the tops of dishes before serving.
Don't substitute ground for fresh in certain dishes. If you are making a Japanese sushi recipe that calls for fresh ginger, the substitution will not work due to the difference in both taste and texture. It's best to leave it out of the recipe rather than call attention to its absence. Ground ginger is best served as a cooked, warming savoury while fresh ginger is an excellent cooling, raw food. This distinction should help you decide when a substitution is appropriate.
Do not substitute fresh ginger for ground in baked goods. The properties and tastes are too different to make a suitable match. If you are missing the spice for biscuits or cakes, try using allspice, nutmeg, ground clove or cinnamon instead.