Direct answer
Joule vs Calorie: What’s the Difference?
Both measure energy. 1 calorie ≈ 4.184 J. Food-label Calorie usually means kilocalorie — with converter links.
Question
What is the difference between a joule and a calorie?
Both measure energy. 1 small calorie (cal) equals about 4.184 joules (J). Food-label Calories usually mean kilocalories.
1 cal
≈ 4.184 J
1 kcal
≈ 4184 J
Food Calorie
Usually 1 kcal
Explanation
The joule is the SI energy unit. The (small) calorie is still common in chemistry and older texts.
Nutrition labels almost always mean kilocalories when they say Calories.
Multiply calories by 4.184 to get joules. Divide joules by 4.184 to get calories.
Important caveat
Confirm whether a source means small calorie (cal) or food kilocalorie (kcal / Cal).