An energy converter changes a quantity of energy or work from one unit into another — kilocalories to kilojoules, kilowatt-hours to megajoules, or BTU to watt-hours. It is used for reading nutrition labels, understanding electricity bills, sizing heating and cooling equipment, and physics work. This tool covers joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts.
The formula. Every value passes through one base unit, the joule. The factors are 1 kJ = 1,000 J, 1 calorie = 4.184 J, 1 kilocalorie = 4,184 J, 1 Wh = 3,600 J, 1 kWh = 3,600,000 J, 1 BTU = 1,055.06 J and 1 eV = 1.602 × 10⁻¹⁹ J. Watch the food-label trap: the "calories" printed on nutrition labels are really kilocalories, so a 250-calorie snack is 250 kcal, not 250 cal.
Worked example. A 2,000 kcal daily diet is 2,000 × 4,184 = 8,368,000 J, which is 8,368 kJ or 2.32 kWh — roughly the electricity a small fridge uses in a day. In the other direction, a 1.5 kW heater running for two hours consumes 3 kWh = 10,800,000 J, and a 12,000 BTU air-conditioner moves 12,000 × 1,055.06 ≈ 12.66 MJ of heat per hour.
Where it's used. Energy conversion links things that rarely appear together: nutrition labels use kcal in the US and India but kJ in Australia and much of Europe, electricity meters bill in kWh, heating and air-conditioning capacity is rated in BTU or kW, and physics and chemistry work in joules with electronvolts reserved for atomic-scale energies. Converting between them turns an abstract number into something comparable.