Hi and welcome
@Chen_Cal
Can I suggest that you complete your profile details, so that members can see what type of diabetes you have, and how you are treating it? Having that information available will help people tremendously when they respond to your questions, and will save them asking the same things over and over again.
Regarding your carb choices in order to observe their portion size impact on your blood glucose, I am afraid you are likely to find this is a very personal thing.
It would be nice to think that 20g of carbs has a nice predictable blood glucose impact. However, in reality, there are lots of different factors in play - fat, fibre and protein eaten at the same time, may slow digestion down. And different carbs hit the blood system at different speeds. This is why glucose is recommended for the treatment of hypos - it hits fast.
Perhaps it would be best if you chose a carb that you regularly eat (rice, or bread, or potato) and then measure it in different portion sizes. However, then there will still be a few other factors affecting the outcome - exercise, stress, hunger, etc. So please don't be surprised if your results vary a bit.