I'm cooking a Romanian meatball soup for 60 people. How much of this soup do I need to feed 60 people? This is the recipe (in Romanian) for the meatball soup.
Here is the ingredient list translated:

Servings: a pot of 5 L

Ingredients - savoriurbane.com

2 carrots

1 parsley root

1 root parsnips

1 celery root (medium)

2 tablespoons of oil

1 onion

2 potatoes

500 ml broth of tomatoes (of the house) or the tomato paste to the box (mashed) or 3-4 fresh tomatoes (summer)

approx. 500 g vegetables of your choice: pod of beans, peas, florets of cauliflower, diced turnip, etc.

1 small bunch of thyme dry


For the meatballs:

500 g minced pork (or mix with beef)
50 g rice (about 2 tablespoons)
1 small onion chopped
1 tablespoon of oil
salt, freshly ground pepper
1 teaspoon of sweet paprika (paprika)
1 teaspoon dry thyme, chopped
1 egg white raw

In addition:

sour cream tart for dres soup
1 raw egg yolk
lemon juice, vinegar, bors or dies
a handful of greenery (leaves of parsley and dill)
optional: chopped leaves of lovage

Additional translations re the amount of water and the total amount of soup the recipe makes:

I added the rest of the roots and I dropped everything with 4 L of hot water.
From the ingredients below we obtained a soup pot of approx. 5 L.
After looking at many very similar recipes (in English) for Romanian sour meatball soup, or Ciorba de Perisoare, I'm inclined to think that this recipe does indeed make 5 liters.

Most all of the recipes I've looked at start with 500g of meat and have pretty much the same ingredient list. This recipe found on  CookingGlory says to :


  Add about 12 to 16 cups of water (about 4l). 


Based on this, I find it easy to believe that the finished soup would easily be 5 liters. (Also, in the translation provided by another user, it shows an amount of 5 liters.)

Also, translated from the link provided in the question:


  From the ingredients below we obtained a soup pot of approx. 5 L. You can reheat without problems and it is tastier every day (kept in the refrigerator lasts for 3-5 days).


And:


  I added the rest of the roots and I dropped everything with 4 L of hot water.


The recipe on Cooking Glory states that it makes 8 - 10 servings. 

So, basic math in hand, 5 L of soup, multiplied by 6 = 30 L of soup. That would give you sixty 500 ml portions.

The link above to the Cooking Glory page also gives a lot of information about the soup and its ingredients.