RE: This is probably a stupid question...
Well, not sure how else you are supposed to work out the calories in a product. That is reading the pack which will tell you how many cals there are per serving, and then work out how much you're going to eat and therefore how much calories you will consume. It's basic maths really! But saying this, you don't need to be 100% dead on with your calorie count per day. If you go a couple over it won't kill you! Just work it out roughly and you'll be fine!