(Not OP, but went through a similar process) The best way (for me at least) was to track my calories, using the food scale to weight things and nutritional lab

(Not OP, but went through a similar process) The best way (for me at least) was to track my calories, using the food scale to weight things and nutritional labels (or looking things up in Google) to figure out the calories. MyFitnessPal for logging everything. If you're asking how to know how many calories you need - search for TDEE calculator online, which will give you an estimate number of calories needed for maintenance, or how much for weight loss, given your height, bodyweight and activity level. But - these are just estimates! Track food intake for a month, see if you went down, if not, start targeting fewer calories (or more if you went down too quickly for your needs).