US Dept of Agriculture nutrient database says 17.49 grams carb per 100g raw potato and skin, of which fibre is 2.1grams, so total net carbs 15.5 g per 100g. Cf baked potatoes below.
That's my preferred database of authority. I subtract the fibre from the carb figure and input the result into my
Carbs & Cals phone app, under 'My Foods'.
While I'm at it, I might as well say that for working out cooked meals, I find Cook & Count very wonderful.
Oh, and also that the various carb counts never quite agree. But they're in the same ballpark, and life's too short. And how do we know we have the archetypal pear, etc. It 's a guide.