This is the formula you need: 1 Calorie [nutritional] = 4.186 8 kilojoules
I am from NZ and nutritional labels here are all in kilojoules too. I usually just round it up and divide the number in kilojoules by 4.19 to get the amount in calories. Hope that helps.
Funnily enough, even though are food are labelled in kilojoules I actually think in calories.
Jan 1st 2016: 142.3lbs (Start Weight)
April 1st 2016: 120.5lbs (and 11.9 inches lost)
Goal Weight: 100lbs