The Calorie King food calculators are very good.
The Australian one is at www.calorieking.com.au/foods/.
The US one is at www.calorieking.com/.
They both have a wide range of foods in their databases, both from supermarkets and from fast food stores. If you are looking for something that is an Australian brand your chances are better with the Aussie site. Likewise for US items and the American site.
The widely accepted figure is 3500 calories = 1 pound of extra weight. This is about “every 3000 KJ adds 0.1 Kg” in metric.