First, measure the length and width of the fridge. Write those numbers down. Then, measure the height of the fridge and write that down as well. Mulitiply these 3 numbers together for the cubic feet.
Measure the height, length and depth of the refrigerator (12 inches in a foot) and multiply them together. Example: length x width x depth = cubic feet.
If you can't find the information anywhere, you'll have to do it manually. Measure the length, width, and height of the INSIDE of your refrigerator, then multiply them together.
One very easy way to figure this out, would be to write down your fridges manufacturer and model number. Go online to the manufacturer's website and look for the model number. It should have all the information there.