Energy Converter

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   What’s great about our Energy Converter

   Fast, accurate conversion of energy values that you can see and drag

   • Free
   • Converts joules, calories, kilowatt-hours, BTU, electronvolts and kilocalories instantly
   • Synced sliders and type-in boxes
   • No sign-up
   • No ads
   • Works offline once loaded
   • No daily limit
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   Choose which units to show

   Use the unit names at the top to show or hide each card. Drag a name or a card’s title to rearrange them; your order is remembered in this browser, and Restore puts the original order back.

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   Drag a slider or type a value

   Move any slider, or type a number into its “Type Value” box, and every visible unit updates instantly. The sliders are logarithmic, so each step along a slider multiplies the value, and one slider covers very small to very large amounts.

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   Widen the range

   Turn on “Wider Range” to widen every slider’s range to cover more extreme values.

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What is Energy?

Energy is the ability to do work or produce heat. It appears as electricity on your bill, calories in food, and fuel in an engine. This converter changes between joules, calories, kilowatt-hours, BTU and electronvolts so you can compare them.

About Joules (J)

The joule is the SI unit of energy and work: the energy used when a force of one newton moves something one meter.

• 1 J = 1 watt for 1 second
• Lifting a small apple one meter takes about 1 joule
• Named after the English physicist James Prescott Joule

About Calories (cal)

The calorie used here is the thermochemical calorie, exactly 4.184 joules: about the energy needed to warm one gram of water by one degree Celsius.

• 1 cal = 4.184 J
• 1,000 cal = 1 kilocalorie (kcal), the “Calorie” on food labels
• Turn on “Kilocalories” to see food Calories

About Kilowatt-hours (kWh)

A kilowatt-hour is the energy used by a 1,000-watt device running for one hour: exactly 3,600,000 joules. It is the unit on electricity bills.

• 1 kWh = 3.6 MJ, or about 3,412 BTU
• A 100 W light bulb uses 0.1 kWh per hour
• An electric car uses roughly 15 to 20 kWh per 100 km

About BTU (BTU)

The British thermal unit used here is the International Table BTU, about 1,055.056 joules: roughly the energy needed to heat one pound of water by one degree Fahrenheit.

• 1 BTU is about 252 calories
• Used for heating and air-conditioning ratings in the US
• A wooden match burns for about 1 BTU

About Electronvolts (eV)

The electronvolt is the energy an electron gains moving through a potential difference of one volt: exactly 1.602176634 × 10⁻¹⁹ joules.

• Used in atomic, nuclear and particle physics
• Visible light photons carry about 1.6 to 3.3 eV
• Chemical bonds have energies of a few eV

About Kilocalories (kcal)

A kilocalorie is 1,000 thermochemical calories, or 4,184 joules. Food energy labeled “Calories” (with a capital C) is in kilocalories.

• 1 kcal = 4.184 kJ
• An average adult needs about 2,000 to 2,500 kcal a day
• Food labels in many countries also show kilojoules (kJ)