Calories is an energy unit which is required to increase the temperature of 1 gram of water by 1 degree celcius at a pressure of 1 atm. On another hand, the joule is a energy unit which is relevant with the total energy exerted on an object when one newton force acts on that object over a distance of one meter. Joule is also one of the derived unit given in the International System of Units.
1 calorie of enegry is equal to 4.184 times the energy in Joules.
