Another question for my jello brain mold

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I went to the store and actually saw the mold. I am buying it today. It's not as big as I thought it was going to be. How much jello should I use. I am not sure exactly how big it is in ounces or whatever. Is there a site I could refrence to see how to make it the right way? We are going to make a sample one to see how it turns out but I was just wondering if anyone else knew when it comes to making a mold using jello?