Energy Converter

How It Works

Energy is the capacity to do work. This converter uses the Joule (J) as its base unit — the SI unit of energy, defined as the work done when a force of one Newton acts through one meter. All energy unit factors are stored as their Joule equivalent.

The Joule connects to other SI units: 1 J = 1 N·m = 1 kg·m²/s². It is a relatively small unit in everyday life — lifting a 100 g apple by 1 meter requires about 1 J, and a human body at rest consumes roughly 80 J per second (80 Watts).

The kilowatt-hour (kWh) is the practical unit of electrical energy on consumer bills. 1 kWh = 3,600,000 J (one kilowatt of power sustained for 3,600 seconds). A typical UK household uses 8–10 kWh per day; a 100W light bulb running for 10 hours uses 1 kWh.

Calories in the context of food are actually kilocalories (kcal). The scientific calorie (cal) is the energy needed to raise 1 gram of water by 1°C = 4.184 J. The dietary Calorie (capital C) = 1 kcal = 4,184 J. A slice of bread contains roughly 80 kcal = 334,720 J.

The British Thermal Unit (BTU) is used in HVAC, heating, and air conditioning in the US. 1 BTU = 1,055.06 J = 0.293 Wh. An air conditioner's cooling capacity is rated in BTU/h.

The electronvolt (eV) is used in atomic and particle physics. 1 eV = 1.60218 × 10⁻¹⁹ J — the energy gained by an electron accelerated through 1 volt. Visible light photons carry about 1.8–3.1 eV; protons at the Large Hadron Collider are accelerated to 6.5 TeV (6.5 × 10¹² eV).

Worked example — Electric car charging:
A car with a 75 kWh battery = 75 × 3,600,000 J = 270,000,000 J = 270 MJ. Charged at 7.4 kW: 75 kWh ÷ 7.4 kW = 10.1 hours to full charge.

Worked example — Calorie counting:
A 2,000 kcal daily diet = 2,000 × 4,184 J = 8,368,000 J = 8.368 MJ = 2.324 kWh per day.

Worked example — Heating with BTU:
A 10,000 BTU/h air conditioner running for 8 hours uses 80,000 BTU = 84,404,800 J = 23.45 kWh.