If I’m making something from scratch, I’d look at the nutritional info on the packet,find the 'carbs per 100g'. column, calculate how many carbs in the amount I'm using (divide the number of carbs in 100g by 100, then multiply by the number of grams you are actually using). Do this for all the ingredients and then add the totals together. (for dumplings, it’s probably going to be just the flour). Then divide the total by the number of portions you are carving the dish up into. Bingo, carbs per portion.