Energy Converter: Calories, Joules, kWh, BTU
Convert between every energy unit in one tool. Joules (J), kilojoules (kJ), calories (cal), kilocalories (kcal, food calories), Watt-hours (Wh), kilowatt-hours (kWh), BTU, and electronvolts (eV). Useful for food labels, electricity billing, HVAC ratings, physics homework, and engineering calculations. Any-to-any conversion supported.
Energy unit converter
1 Kilocalorie = 4.184 Kilojoule
Energy reference values
Real-world energy amounts in different units.
| Source | kcal | kJ | kWh | BTU |
|---|---|---|---|---|
| 1 Calorie (kcal, food) | 1 | 4.184 | 0.00116 | 3.97 |
| Apple (~100 kcal) | 100 | 418 | 0.116 | 397 |
| Daily diet 2000 kcal | 2,000 | 8,368 | 2.32 | 7,937 |
| 1 kWh (small fridge/day) | 860 | 3,600 | 1 | 3,412 |
| 10,000 BTU AC for 1 hr | 2,521 | 10,551 | 2.93 | 10,000 |
| 1 liter petrol | 7,750 | 32,400 | 9.0 | 30,720 |
| Marathon (run 42 km) | 2,800 | 11,715 | 3.26 | 11,107 |
| 1 ton refrigeration / day | 68,920 | 288,394 | 80.1 | 273,500 |
About energy
What is energy?
Energy is the capacity to do work, measured in Joules (J) in the SI system. One Joule equals one Newton-meter of work, or roughly the energy to lift a 100-gram chocolate bar one meter against gravity. The Joule is small for everyday purposes, so practical energy quantities use multiples like kilojoules (kJ), megajoules (MJ), or specialized units like calories (food), kilowatt-hours (electricity), and BTU (heating and cooling).
Calories vs Calories (confusing!)
"calorie" (lowercase) is a small physics unit: the energy to raise 1 gram of water by 1°C. "Calorie" with a capital C, or kcal, is 1000 of those, the energy to raise 1 kg of water by 1°C. Food labels always use kcal but typically write "Calories" or "cal" without making the distinction clear. A 2,000 Calorie diet means 2,000 kcal = 8.37 MJ = 2.33 kWh. The calculator labels them clearly: "cal" = small physics calorie, "kcal" = food Calorie.
The kilowatt-hour (kWh)
Electricity is sold by the kilowatt-hour, defined as 1000 watts of power used for 1 hour. So a 100-watt light bulb running for 10 hours uses 1 kWh. A typical Pakistani household uses 200 to 800 kWh per month (more in summer with AC). Use our electricity bill calculator for Pakistan slab-based bill estimates. 1 kWh = 3.6 MJ = 860 kcal = 3,412 BTU.
BTU: heating and cooling
The British Thermal Unit is the energy to raise 1 pound of water by 1°F. 1 BTU = 1,055 J. Air conditioners are rated in BTU per hour: a 12,000 BTU/hour AC = 1 ton of refrigeration = 3.5 kW of cooling power. Home furnaces are rated in BTU per hour for heat output. The BTU is mostly used in the US; outside the US, kilowatts (kW) of heating or cooling power are more common.
Energy in food
Macronutrients carry the following energy: protein 4 kcal/g, carbohydrate 4 kcal/g, fat 9 kcal/g, alcohol 7 kcal/g, fiber 2 kcal/g. Multiply the gram amount by the per-gram value and sum to get total food energy. An adult typically needs 1,800 to 2,800 kcal/day depending on age, sex, body size, and activity. Use our calorie calculator for personalized estimates.
Energy in fuel
Petrol: about 32.4 MJ/L (9 kWh/L, 7,750 kcal/L). Diesel: about 36 MJ/L (10 kWh/L). Natural gas: about 35 MJ/m³. Coal: 24 to 32 MJ/kg. Wood: 15 MJ/kg dry. Internal combustion engines convert about 25 percent of fuel energy to useful motion; the rest is lost as heat and friction.
The electronvolt and physics scales
The electronvolt (eV) is used in physics for atomic and subatomic energy scales. 1 eV = 1.602 × 10⁻¹⁹ J. Visible light photons have 1.5 to 3 eV of energy. Chemical bonds are typically 1 to 10 eV per bond. X-rays are keV (thousands of eV). Nuclear reactions involve MeV (millions of eV). At the very large end: total Earth annual energy consumption is around 600 exajoules.
Useful conversions to remember
1 kcal = 4.184 kJ. 1 kWh = 3.6 MJ = 860 kcal. 1 BTU = 1.055 kJ. 1 cal = 4.184 J. These four relationships cover most everyday conversions. The calculator handles them all to 6 significant figures.
Energy used in exercise
Walking (5 km/h): 250 kcal/hour. Cycling (20 km/h): 500 kcal/hour. Running (10 km/h): 700 kcal/hour. Swimming (vigorous): 600 to 800 kcal/hour. Strength training: 300 to 500 kcal/hour. Sleeping: 60 to 80 kcal/hour (basal metabolic rate continues). Use the calculator to translate these to kJ or kWh for energy budgeting.
Multiply calories by 4.184 to get kilojoules (kJ). So 100 kcal (food calories) = 418.4 kJ. Note that food labels use "calories" to mean kilocalories (kcal); 1 food calorie = 1 kcal = 1000 thermochemical calories. The calculator handles both.
A "calorie" (lowercase) in physics is 4.184 Joules, the energy to raise 1 gram of water by 1 degree Celsius. A "Calorie" (capital C, also called kcal) is 1000 of those, the energy to raise 1 kg of water by 1 degree. Food labels always use kcal but write it as "Calories" or just "cal", causing confusion. A 2,000 "Calorie" daily diet means 2,000 kcal or 2 million physics calories.
1 kWh = 3,600,000 Joules (3.6 megajoules). The kWh is the standard unit for electricity billing because it represents one kilowatt of power used for one hour. A 100-watt light bulb running for 10 hours uses 1 kWh.
British Thermal Unit, the energy to raise 1 pound of water by 1 degree Fahrenheit. 1 BTU = 1,055 Joules. BTUs are used in US heating and cooling specifications (air conditioners are rated in BTU/hour, and home heating systems in BTU). 12,000 BTU/hour cooling = 1 ton of refrigeration.
Joule (J), Kilojoule (kJ), calorie (cal), kilocalorie (kcal), Watt-hour (Wh), Kilowatt-hour (kWh), BTU, and electronvolt (eV). Any-to-any conversion supported.
2000 kcal (food calories) = 2,000,000 thermochemical calories (cal) = 8,368 kilojoules (kJ) = 7,937 BTU. Most food labels in the EU show both kcal and kJ. Australian and New Zealand labels often use kJ alone (a 2000 kcal diet is 8,368 kJ).
Roughly 60-80 kcal per kilometer (or 100-130 kcal per mile) for an average adult. A 5K (3.1 mile) run burns 300 to 400 kcal. A marathon (42.2 km) burns 2,500 to 3,500 kcal. Heavier runners burn proportionally more.
A tiny unit of energy used in physics: 1 eV = 1.602 × 10⁻¹⁹ Joules. It is the energy a single electron gains when accelerated through one volt. Used in particle physics (electron beams, X-rays) and chemistry (bond energies). Visible light photons have energies of 1.5 to 3 eV; nuclear reactions involve MeV (million eV).
In kilowatt-hours (kWh). Your electricity meter shows total kWh consumed. The utility multiplies kWh by the per-unit rate. In Pakistan the per-kWh rate is around Rs 30 to 50 depending on slab; in the US around $0.10 to $0.30 per kWh; in the UK around £0.27 per kWh. Use our electricity bill calculator for slab-based estimates.
About 32.4 megajoules (MJ) or 9 kWh of chemical energy. Of this, about 25 percent is converted to useful motion in a typical petrol engine (the rest is lost as heat and friction). So 1 liter of petrol gives roughly 2.25 kWh of actual movement energy.
Protein and carbohydrates: 4 kcal per gram. Fat: 9 kcal per gram. Alcohol: 7 kcal per gram. Fiber: 2 kcal per gram. Multiply each by your serving size and add to get total food energy. The calculator converts between food calories (kcal) and other energy units.
No. Lowercase "calorie" = 4.184 J. Capital "Calorie" = kcal = 4,184 J = 1000 small calories. Food labels are always in kcal even when written as "calories" or "cal". The calculator labels them clearly to avoid confusion: "cal" is the thermochemical (small) calorie, "kcal" is the food (large) calorie.
Yes. All values stay in your browser. Nothing is sent to a server, logged, or shared. You can use the calculator offline once the page has loaded.