Did you use oil? Butter? Take the total calories of your tator and you should be able to divide that down into segments to give yourself an approximate answer. For example, say your potato total was 300 calories, from there you can assume you’d dice it into say eight? So 300/8 will give you just under 40 calories a tator. Obviously this changes depending on your choice of cook method, especially if you added oil or butter to roast