As stated, the serving size is, typically, listed on the package, however, if you're eating a food that's not packaged, you can find serving sizes listed online.
For instance, a serving of meat is 3-4 oz or you can estimate about the size of a deck of playing cards; a serving of rice is about 1/2 cup or the size of a cupcake wrapper. A teaspoon is about the size of a dice; a tablespoon is about the size of the end of your thumb; a pancake, the size of CD, a serving of cheese, the size of a 9V battery, etc.
You can google serving sizes and come with a variety of sites that will give you actual serving sizes for a variety of foods, along with how to estimate, if you're eating out and don't have a way to measure exactly.
Non starchy fresh/frozen veggies are, typically, unlimited in quantity, unless they are covered with cream or cheesy sauces or other high fat coatings.
Many times the serving is posted on the container. Eg. Raisen brand 1 serving =1cup. Ideally this information can be found on the back or side of the container.
Many times the serving is posted on the container. Eg. Raisen brand 1 serving =1cup. Ideally this information can be found on the three back or side of the container.
A serving varies from the type of package you buy the food in,and if you bought packaged goods the serving size is on the package. If it's a particular type of fruit or whatever, you can look up the serving size on the internet.
It will usually say some where like this dish serves 6. Then you just calculate by devision. How many ounces = one serving.
They sometimes do this intentionally so people think the product has less calories.