When I seriously started juicing in 2002, I followed the instructions in Norman Walker's books. I had to get so many ounces of carrot, celery, etc. to make whatever juice. Nowadays, I simply look at what I have, what I want, and how much. For example, this morning, I juiced cabbage, celery, cucumber, green apple, small tomatoes, and squeezed fresh lemon juice. Tasted fantastic!
When people ask me how much of whatever they want to take, I smile - how do I know? All I know is that you have to start from a little quantity and see how your body responds. We all have our own constantly changing lab inside and outside - some cell receptors could be clogged, some needing nutrition. A good example is how we smell things - we all have our preferences. And when our nose is clogged somewhat, we may detect only a spectrum of the scent.
All I'm trying to do is listen to my own body, be present. Do I want to drink? Then I will.
To Health!
:)