What does everyone do if you are eating pasta/noodles (corkscrew, elbow, shells, etc.) that someone else has made for you? How do you calcuate the calories? It is hard even to estimate the amount.
If it's stuff you make yourself then take twenty minutes and measure / weigh the dry pasta against the nutrition facts label on the package. Then weigh / measure the cooked amount.
That should give you a good idea when you need to eyeball portions in the future.