Energy Calculator

Calculate kinetic energy, potential energy, E=mc² and work

What is it and how does it work?

Energy is measured in many units across different domains: joules (SI unit for physics), kilowatt-hours (kWh, used for electricity billing), calories (nutrition and thermodynamics), BTU (British Thermal Units, used in HVAC and US energy contexts), and electronvolts (eV, used in particle physics). Converting between them correctly is essential for comparing energy costs, understanding nutrition labels, calculating appliance consumption, and working with engineering specifications.

This calculator converts between all major energy units and also solves the fundamental energy equations: kinetic energy (½mv²), potential energy (mgh), electrical energy (Power × Time), and thermal energy (mcΔT). Whether you're estimating a monthly electricity bill, calculating the energy in a chemical bond, or comparing the energy content of fuels, this tool provides instant conversion and calculation.

Common use cases

• Electricity cost: a 60W bulb running for 8 hours uses 0.48 kWh; at $0.13/kWh that's $0.062/day or $22.63/year — compare with a 9W LED using 0.072 kWh ($3.39/year).
• Nutrition comparison: a 250 kcal chocolate bar contains 1,046,500 joules of chemical energy — enough to lift a 70 kg person about 1,526 metres (ignoring efficiency losses).
• HVAC specification: a 12,000 BTU/hour air conditioner is about 3.5 kW of cooling capacity — use the conversion to compare with equipment rated in watts or kilowatts.

Frequently asked questions

What is the difference between energy and power?

Energy is the total amount of work done or heat transferred (measured in joules, kWh, etc.). Power is the rate at which energy is used or produced (measured in watts = joules/second). A 100W light bulb uses energy at a rate of 100 joules per second. Running it for 10 hours uses 3,600,000 joules = 1 kWh of energy.

What is the difference between a calorie and a Calorie (kcal)?

A calorie (lowercase) is the amount of energy needed to raise 1 gram of water by 1°C. A Calorie (uppercase, also kilocalorie or kcal) is 1000 calories — the unit used on food nutrition labels. When a food label says "250 Calories", it means 250 kcal = 250,000 small calories = about 1,046,000 joules.

How do I calculate monthly electricity cost from appliance wattage?

Formula: cost = (wattage / 1000) × hours_used × electricity_rate. Example: a 2000W electric heater running 5 hours/day for 30 days at $0.15/kWh: (2000/1000) × 5 × 30 × $0.15 = $45/month. The key conversion is: 1 kWh = 1000 Wh = 3,600,000 joules.

What is an electronvolt (eV) and where is it used?

An electronvolt is the energy gained by a single electron accelerating through 1 volt of electric potential. 1 eV = 1.602 × 10⁻¹⁹ joules. It's the natural energy scale for atoms, molecules, and particle physics: visible light photons carry 1.8–3.1 eV; chemical bond energies are 1–10 eV; X-ray photons are thousands of eV (keV); particle accelerator beams reach billions of eV (GeV, TeV).

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