To get an accurate carb count of a potato, you must cook it first, then measure the inside, and then weigh it. If you are trying to lose weight, you must weigh the inside, then cut the potato in half, then measure the inside.
The breakdown of carbs and calories in potatoes is quite simple, and you can get away with eating 150 grams of potato for 25 grams of carbs and 200 calories.
Potatoes are an excellent alternative to white rice, and sweet potatoes are high in fiber. Sweet potatoes have a higher carb count than red potatoes, however.