What is the biggest safe container for soup? What is the biggest safe container for soup?  The soup comes out of the slow cooker at a high temperature (not measured), but I need to refrigerate it for storage, and that means that it needs to be cooled down rapidly.  That means small containers.

How small should the containers be?  They are standard plastic — I don't have anything fancy.

Currently, I put them into containers and place them in the fridge, but that is all.  Should I cool them in water?
You said the containers are plastic so you have already determined the size of the container. If the containers are clean and sanitary then they are safe. The only important part is cooling the soup down fast enough so it stays out of the "danger zone"; that is, above 40F for more than two hours. So however long that takes will take experimentation or applied physics knowledge or experience.

You can gain experience by heating some water to a simmer as you would for soup (I think). Then see how long it takes you to cool it to 40F. If you can do that in less than two hours, you're cool and safe.