A serving of pasta is two ounces (56g) of dry pasta. When measuring dry pasta though, it’s not easy to get the exact amount. Depending on the shape, pasta will approximately double in size when cooked, so the amount of cooked pasta can vary.
For smaller shapes like penne, elbows, rotini, and bowties, approximately ½ cup of dry pasta is two ounces, so that’s a good rule of thumb. A 12 ounce box of these shapes will have six servings.
For long pastas like spaghetti, angel hair, linguini, and fettuccini, your best bet is to hold the pasta on end to measure it. Two ounces of dry pasta is approximately 2/3 of an inch across, or one serving. A 16 ounce box of these shapes will have eight servings.