Energy Converter

Energy is the capacity to do work, and the beauty of the joule (J) is that it puts every form of energy on one scale: the calories in food, the kilowatt-hours on your power bill, the BTU on a furnace, all the same quantity in different clothing.

Key relationships:

• 1 kJ = 1,000 J
• 1 cal = 4.184 J
• 1 kcal = 4,184 J (a food Calorie)
• 1 Wh = 3,600 J
• 1 kWh = 3,600,000 J
• 1 BTU = 1,055.06 J

For scale:

• A food Calorie: 4,184 J
• A 100 W bulb for one hour: 100 Wh (360,000 J)
• A typical US household per day: about 30 kWh
• A gallon of gasoline: about 139 MJ

The calorie causes more confusion than any other energy unit. The “calorie” on a food label is really a kilocalorie, 1,000 of the small calories used in chemistry, which is why it’s sometimes written with a capital C. A 200 Calorie snack holds 200,000 chemistry calories, about 837 kJ.

Don’t mix energy up with power. Energy (joules, kWh) is the total amount; power (watts) is the rate of using it. A kilowatt-hour is energy, what you get from one kilowatt running for one hour. Your electric bill charges for energy in kWh, not for power, which is why leaving a small device on for days can cost more than a big appliance used briefly.