Convert kilojoule to watt hour

The calorie of food labels is really the kilocalorie: 1 kcal = 1,000 cal = 4.1868 kJ, the heat that warms a kilogram of water by one degree. Nutrition labels in the EU must give both kJ and kcal, the US gives 'Calories' with a capital C meaning kcal, and the adult reference intake is 2,000 kcal, about 8,400 kJ. A slice of bread is around 80 kcal, an hour's brisk walk burns about 300.

The watt (W) is a unit of power, the rate at which energy is used or produced. The watt-hour (Wh) is a unit of energy, one watt sustained for one hour, and is what this page converts: a 2 kW heater running for 3 hours uses 6 kWh, and an electricity bill counts kWh. 'Watts per hour' (W/h) would be a rate of change of power, is rarely needed, and is not the same thing as a watt-hour.