With a portion of chicken and gravy being about 1 1/2 cups. You can serve about 48 people with each 18 quarts. for 300 people you will then need more than 6 1/4 18 qt roasters. So, 7 roasters will be what you need for a minimum.
Most 18 quart roasters suggest you stick with 16 pounds or less. It depends somewhat on the shape of the bird. But it cooks best if there is 1 inch or more between each wall and the lid, and the turkey.
1 quart is equal to 2 pints.
A quart of chicken salad typically weighs around 1 to 1.5 pounds, depending on the ingredients and how densely it's packed. Generally, a quart is about 4 cups, and chicken salad can vary in density due to factors like added vegetables or dressing. For a more precise measurement, it's best to weigh the salad directly.
Common sizes in slow cookers are the 3, 4 and 5 quart size. For a family of four, buy at least a 4 quart unit. Depending on your family's appetites, a 6 quart or even larger unit might be appropriate.
quarters
A quart is 32 ounces. I would serve 4 oz portions to 8 people.
A Rival Roaster is an electric roasting pan. The 18 quart version can hold an 18 lb turkey. It costs around $50 to purchase. The main benefit to owning one, is that the oven is free to cook pies or side dishes during Thanksgiving.
What is a "people quart"
I would guess a quart of soup feeds three. I think one can is considered a serving, and a can of soup is typically about 10 ounces. A quart is 32 ounces.
A quart of milk typically serves around 4 people, with each person receiving approximately 1 cup of milk.
Some delicious recipes that can be made using a 4-quart slow cooker include beef stew, pulled pork, chicken curry, chili, and vegetable soup.
"Quart" means 4, so there are 4 people in a quartet.