If you are following a diet plan where they have allowed foods, then you'll need to follow the way
they work that plan.
How low carb and how strictly you manage your diet is your choice and will depend on you personally, e.g. what your body can handle, and whether you need to lose weight, reduce high glucose levels, or both.
In theory yes you
may need to count all the carbs you eat, and this should be the carbs in
your chosen portion size, not carbs per 100grams weight or the manufacturers' - often ridiculously small - suggested portion size And diabetics on insulin may need to be strict with their counting if they have to calculate the amount of insulin they need for their meals as their health and safety may well depend on this.
If you are planning to start off with a
very low carb/ketogenic diet to lose weight, then certainly every carb
will need to be counted to keep your intake low enough to get into fat burning mode. You can check online for the Atkins diet to find out more about this in their induction mode information, where you're limited to certain foods (e.g. no fruiit or nuts), and to 20 grams carbs a day for a short time to kick start ketosis. So the lower you choose to go the more important accurate assessment may need to be.
I currently tend to do similar to
@BooJewels and once I have an idea of the carbs in my commonly eaten foods, then I'll "guesstimate" or do a rough calculation. And with fruit and vegetables it can only be so, as nature doesn't count carbs, and things like variety, growing conditions, or ripeness may well affect the actual carb content of grown foods. So I'm generally going to be eating between 30-50 grams carbs a day, which gives me some "wriggle room" food and portion size wise, and allows me the variety of food that I need for a healthy
and sustainable diet - and still keeps me nicely low carbing. My meter will tell me if I'm getting off track.
Robbity