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Energy Converter

Energy appears in many units across different domains: joules in physics, calories in nutrition, kWh in electricity, BTU in HVAC, and eV in atomic physics. Our converter handles all energy units and puts the numbers in context — how many joules in a calorie? How many kWh to power a laptop for a day?

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About the Energy Converter

Energy appears in many units across different domains: joules in physics, calories in nutrition, kWh in electricity, BTU in HVAC, and eV in atomic physics. Our converter handles all energy units and puts the numbers in context — how many joules in a calorie? How many kWh to power a laptop for a day?

How to use it

  1. Enter a value and select the unit: joules, calories (small and large), kWh, BTU, eV, erg, foot-pounds.
  2. See instant conversions across all energy units.
  3. Use the "context" panel to compare the energy amount to familiar reference points.

Formula & methodology

1 calorie (small/thermochemical) = 4.184 joules. 1 Calorie (food/large, kcal) = 4,184 joules = 1.163 Wh. 1 kWh = 3,600,000 joules = 3,412 BTU. 1 BTU = 1,055.06 joules. 1 eV = 1.602 × 10⁻¹⁹ joules. 1 erg = 10⁻⁷ joules. 1 foot-pound = 1.356 joules.

Common use cases

  • Nutrition: understanding that 1 food Calorie = 1 kcal = 4,184 joules
  • HVAC: BTU ratings for air conditioners and heaters
  • Electricity: kWh for energy consumption and billing
  • Physics: joules and electron volts for atomic and particle physics
  • Chemistry: kilojoules per mole for reaction enthalpy

Frequently asked questions

Two definitions: small calorie (cal) = energy to raise 1g of water by 1°C = 4.184 J. Large Calorie (Cal or kcal) = energy to raise 1kg of water by 1°C = 4,184 J. Food labels use the large Calorie (kcal), written with a capital C. A 200-Calorie snack has 200 kcal = 200,000 cal = 836,800 joules. This is a consistent source of confusion in nutrition and physics.
1 kWh (kilowatt-hour) = 3.6 megajoules = 3,412 BTU. In practice: running a 1,000W hair dryer for 1 hour; charging a smartphone ~50 times; driving an electric car about 3–4 miles; heating 1 liter of water from room temperature to boiling about 50 times. At $0.16/kWh US average, 1 kWh costs 16 cents.

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