Authentic Italian pasta dishes use no more than a quarter cup of red spaghetti sauce per serving, while traditional American spaghetti uses about 1/2 cup of sauce in the middle of the spaghetti. So, for each serving, you need anywhere from 2 to 4 ounces of spaghetti sauce.
For each person, cook at least 2 ounces of dry pasta. If one person is likely to eat more than one serving, make sure to make enough sauce and pasta. The more hearty and thick the sauce, the less pasta each person needs. Thinner sauces need more pasta and less sauce than chunky sauces because they coat the pasta better.