Energy Converter

Scientific, food and electrical energy

This converter covers joules and kilojoules, calories and kilocalories (food Calories), watt-hours and kilowatt-hours, electronvolts for physics, plus BTU and foot-pounds. It bridges nutrition labels, electricity bills and physics problems in one place.

All conversions use exact definitions (1 cal = 4.184 J, 1 kWh = 3.6 MJ), so results are reliable across every domain.

Common energy conversions

• Kilocalories to kilojoules for nutrition
• kWh to joules for electricity
• BTU to joules for heating and cooling

Key features at a glance

• Scientific units: joules, kilojoules, electronvolts
• Nutritional units: calories and kilocalories (food Calories)
• Electrical units: watt-hours and kilowatt-hours
• Thermal units: BTU and foot-pounds
• Live conversion table updates as you type
• Runs entirely in your browser, even offline

Energy is one quantity in many disguises

Energy takes many forms — heat, motion, electricity, chemical, nuclear — but it is a single physical quantity, which is why all these units are interchangeable. The SI unit is the joule, defined as the energy used when a force of one newton acts over one meter. Every other energy unit, however different its origins, can be expressed exactly in joules: one calorie is 4.184 joules, one kilowatt-hour is 3.6 million joules.

This universality is what makes an energy converter so powerful. The food Calorie on a nutrition label, the kilowatt-hour on an electricity bill, and the joule in a physics textbook all measure the same thing. Converting between them reveals surprising connections — the energy in a candy bar, for instance, could power a small device for hours — because underneath the different units lies one common currency of energy.

Calories, Calories, and nutrition

Nutrition is a notorious source of confusion because of the calorie. The 'calories' listed on food labels are actually kilocalories — one food Calorie (with a capital C) equals 1,000 small calories. So a 250-Calorie snack contains 250,000 of the calories a physicist would count, or about 1,046 kilojoules. Most of the world labels food energy in kilojoules, while the United States uses Calories, which is why the same product shows very different numbers in different countries.

This converter makes the relationship explicit, letting you move between food Calories (kilocalories) and kilojoules so you can read any nutrition label wherever it comes from. Understanding that a label's 'calorie' is really a kilocalorie clears up the apparent mismatch and helps when comparing products, tracking intake, or following a recipe that uses unfamiliar energy units.

Electrical energy and your bill

Electricity is sold by the kilowatt-hour, the energy of a one-kilowatt appliance running for one hour. This is a unit of energy, not power, and it is what determines your electricity bill. Converting kilowatt-hours to joules — one kWh equals 3.6 megajoules — connects everyday utility usage to the scientific scale and helps make sense of appliance energy ratings.

Knowing these conversions is practical for estimating running costs and comparing energy sources. A space heater rated at 2 kW running for three hours uses 6 kWh; expressed in joules that is over 21 million, which underscores how much energy heating consumes. The converter bridges the electrical, scientific, and thermal worlds so you can reason about energy consistently across your bill, your appliances, and any calculation.

Tips for converting energy

• Food 'calories' on labels are actually kilocalories (1 Cal = 1,000 cal)
• One kilowatt-hour equals exactly 3.6 megajoules
• One calorie is 4.184 joules; one kilocalorie is 4.184 kilojoules
• BTU is common for heating and cooling; 1 BTU is about 1,055 joules
• Use kilojoules to compare nutrition labels from different countries

Why choose our energy converter?

Our converter is completely free with no signup, no limits, and no subscription. It runs entirely in your browser, so conversions are instant, it works offline, and the values you enter never leave your device.

It is one of more than 200 free tools on ToopTools, and you can pin it to your My Workspace, a personalized workspace where you keep the tools you use most in a single dashboard. Beside the other unit converters, it bridges nutrition, electricity, and physics energy units in one place.

Common use cases

People use the energy converter to read nutrition labels by switching between food Calories and kilojoules, to understand electricity usage by converting kilowatt-hours, and to solve physics problems in joules and electronvolts. It connects units that usually live in separate worlds.

Engineers and HVAC professionals convert BTU for heating and cooling, students work in joules and calories for science, and anyone comparing appliance energy ratings or food products across countries uses it. Because every unit appears at once, a single energy value reads across nutrition, electrical, and scientific scales together.

Is the energy converter free?

Yes. It is completely free with no account, no sign-up, and no usage limits. Convert as much energy as you like at no cost.

Are food calories the same as scientific calories?

No. A food Calorie (capital C) is actually a kilocalorie, equal to 1,000 scientific calories. So a 200-Calorie food contains 200 kilocalories, or about 837 kilojoules.

How many joules are in a kilowatt-hour?

One kilowatt-hour equals exactly 3.6 megajoules, which is 3,600,000 joules. This is the energy unit your electricity bill uses, representing a one-kilowatt load running for one hour.

How do I convert kilocalories to kilojoules?

Multiply kilocalories by 4.184 to get kilojoules. For example, a 500-kcal meal is about 2,092 kilojoules. The converter does this exactly, which is handy for reading nutrition labels.

What is a BTU?

A British Thermal Unit is the energy needed to raise one pound of water by one degree Fahrenheit, about 1,055 joules. It is widely used for heating, cooling, and air-conditioning capacity.

Are my conversions kept private?

Yes. Everything is computed in your browser and nothing is uploaded, so the values you enter stay private and the tool works without an internet connection.

How do I convert joules to calories?

Enter a value in joules and choose calories as the target, and the converter shows the result instantly. It also handles kilojoules, kilocalories, watt-hours, kilowatt-hours, and BTUs, so you can switch between scientific, food, and electrical energy units in one step.

Does the energy converter work offline?

Yes. The conversion runs entirely in your browser, so once the page has loaded the tool works without an internet connection, and nothing you enter is uploaded — it stays private on your own device.