How many calories equals how many joule?

1 calorie = 4.184 joules

So, 200calories * (4.184joules/1calorie) = 200*4.184 joules= 836.8 joules

Since the category of this question is nutrition, I will point out that "calories" on food are actually "Calories". Notice the capital "c". It makes a difference. "Big c" calories are actually calories * 1000!

A 100 Calorie snack isn't 100*4.184 = 418.4 Joules, it is 100,000 *4.184 = 418,400 Joules!