As a bariatric patient, your main goals are 64 ounces SF/calorie free beverages per day, and at least 60 grams of protein.
How do you know how much you are getting in each day unless you are measuring?
The best way to determine the amount of food in a serving is to measure it out. And precision is key: If you eat too little, you could rob your body of the nutrients it needs. And if you eat too much, you could ingest too many calories, and eventually put on weight.

For beverages:
If you have a favorite cup/tumbler, know how many ounces it holds.
Ounces are listed on all bottled/canned beverages.

For food:
Use a scale for protein. It sounds tedious, but after you get used to it, you will be a pro.
Use appropriate measuring cups.
Read labels.

You don’t know what you don’t know. Measuring your beverages and protein, reading labels and keeping a journal will help you stay on track.