How to gauge orzo's change in volume from dry to cooked for a soup? I am working on a scratch chicken, vegetable orzo soup. I'm not following any particular recipe, just shooting from the hip. I usually come up with a good meal but the problem I always run into though is with gauging how much pasta (or barley or rice) to add to a soup and keep it at all balanced. 

Protein and veggies are easy since those ingredients usually do not change in size during cooking but whenever I use a starch that changes in volume while cooking I end up with a soup that is either starch heavy (too much grain or pasta) or starch light (too much veggie and protein in relation to the starch.)

So my basic question is: I have a half cup of dry orzo sitting at the ready. How many cups will that half cup turn into after cooking in soup stock? I am using orzo right now but would also be interested in seeing similar information for other types of pasta and any soup-suitable grains. Any rules of thumb or ideas for different approaches would be appreciated as well.

Thanks!
It will double in size when it is cooked, however the longer it is kept in the liquid the bigger it will grow until ultimately all liquid has been absorbed. 

A trick is to cook it separately, drain it, and toss with olive oil so it doesn't clump. Then, add it to the rest of the soup, stirring well just before serving.