Because it is based on calories, dietary fiber and fat, you can not go exactly by calories but a good estimates in 1 point per 50 calories. If you look at a 100 calorie pack, even if it has no fiber it will be 2 points if it does not have more than 6 grams of fat. Like I said it is not exact but a good extimate if you don't have a listing or a slide to calculate
As was previously stated, point values are based on a combination of calories, fat and fiber. For example, Campbells' Chicken Soup in Hand is 80 calories, with 2 g. fat and 2 g. fiber - and it comes out as 1 point. Your best bet is to use your tracker.