I'm currently dieting again, and the only way that I've been able to properly portion calories is to weigh nearly everything I eat and then add the numbers together in Google Sheets.

Eyeballing a portion of a lot of food can be nearly impossible to determine how much food you actually got, but weight is fairly straightforward and objective (at least to an ounce or so of granularity for most kitchen scales, which is good enough for dieting).