You can use an app like my fitness Pal to log your food and there is a setting somewhere that will show your percentages ... Can't remember where exactly - sorry. Watch out for some of the values of food on there that have been put in by other users - always check against the packaging
I used to have a notebook in which I wrote down the percentages for various foods. I use net carbs, so minus the fibre.
I used raw weights, so I could just put a pan on the scales, zero it and then add in the food up to the amount I worked out - if something is 10 percent carbs then every 10 gm of the food is a gm of carb, 5 gm of carb, 50 gm of food - I did keep a sliderule in the kitchen so as to work out the more difficult ones.
I don’t work percentages as the fat and fiber and protein amounts all contribute. I just only eat 20 g or less per day. Carbs are such a wild card, FOR ME