How to convert between calories and kilojoules?

1 kilocalorie (kcal) = 4.184 kilojoules (kJ). Food packaging typically labels energy in kilojoules; to convert to kilocalories, divide by 4.184. For example, 2000 kJ ≈ 478 kcal.

How many joules is 1 kWh of electricity?

1 kWh of electricity = 1 kilowatt-hour (kWh) = 3600 kilojoules (kJ) = 3,600,000 joules (J). kWh is the common unit for measuring electrical energy.

What is the difference between kilocalories and calories?

1 kilocalorie (kcal) = 1000 calories (cal). The "calories" commonly mentioned in daily life usually refer to kilocalories (large calories), the food energy unit. 1 kcal equals the heat needed to raise 1 kg of water by 1°C.

🔋 Energy Converter

Convert between Joule, kJ, calorie, kcal, kWh, and BTU

Enter Value

Input Unit

Joule (J)4184

Kilojoule (kJ)4.184

Calorie (cal)1000

Kilocalorie (kcal)1

Kilowatt-hour (kWh)0.00116

BTU3.96588

* Conversion: 1 kcal = 4.184 kJ, 1 kWh = 3600 kJ, 1 BTU ≈ 1.055 kJ

* 1 kJ = 1000 J, 1 kcal = 1000 cal

Energy Converter Guide

This tool converts between joules (J), kilojoules (kJ), calories (cal), kilocalories (kcal), kilowatt-hours (kWh), and BTU. Enter a value and select the unit to automatically convert to other units.

Energy conversion is commonly used in nutrition, electricity, heating, and fitness.

Energy Unit Conversion Reference

Conversion relationships: - 1 kcal = 4.184 kJ = 4184 J - 1 kWh = 3600 kJ = 3,600,000 J - 1 BTU ≈ 1.055 kJ = 1055 J - 1 cal = 4.184 J

Common conversions: - 1 kWh = 3600 kJ = 860.4 kcal - 1 bowl of rice (200g) ≈ 232 kcal ≈ 971 kJ - 1 hour jogging ≈ 400 kcal ≈ 1674 kJ

Note: - Food labels use "Calories" (capital C) = kcal - 1 Calorie (kcal) = 1000 calories (cal) - US food labels use Calorie (capital C) = kcal

FAQ

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Energy Converter Instructions

The energy converter supports conversion between six commonly used energy units: Joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), kilowatt-hour (kWh), and BTU. Enter a value and select the source unit to see the equivalent value in all units.

Energy is one of the most fundamental concepts in physics — the capacity to do work, the measure of heat transfer, the driving force of chemical reactions. Different fields prefer different energy units: physicists use joules, nutritionists use calories, electrical engineers use kilowatt-hours, and HVAC engineers use BTU. This tool unifies these cross-disciplinary needs.

Energy Unit Conversion Relationships

【International System of Units (SI)】
1 kJ = 1000 J
1 J = 1 N·m = 1 W·s (1 watt × 1 second)

【Thermal Units】
1 kcal (large calorie/kilocalorie) = 4184 J = 4.184 kJ
1 cal (small calorie) = 4.184 J (Note: food "calories" usually refer to kcal)
1 BTU ≈ 1055.06 J ≈ 1.055 kJ

【Electrical Units】
1 kWh = 3,600,000 J = 3600 kJ = 860 kcal

【Reference Values】
1 ton TNT energy ≈ 4184 kJ (≈1 Mcal)
Daily human energy requirement ≈ 2000-2500 kcal

Conversion Examples

📋

【Example 1】Food calories A meal of about 800 kcal = ? kJ / kWh = 800 × 4.184 = 3347.2 kJ = 3347.2 / 3600 ≈ 0.93 kWh ≈ Less than 1 kWh of electricity! But the body can't "recharge" 【Example 2】Electricity bill calculation Air conditioner running 1 hour consumes 1.5 kWh = 5400 kJ = 1290 kcal At $0.10/kWh: cost is $0.15 【Example 3】Fuel heating value 1 kg gasoline complete combustion ≈ 44,000 kJ = 10,516 kcal ≈ 12.22 kWh Equivalent to 1.5L gasoline driving a car about 25 km 【Example 4】Exercise calorie burn Running 30 min (8 km/h): about 300 kcal = 1255 kJ ≈ 0.35 kWh ≈ Need to run 5.5 more 30-min sessions to burn off an 800 kcal meal

Important Notes

💡

- "Calories" on nutrition labels usually refer to kilocalories (kcal), not small calories (cal). 1 kcal = 1000 cal - "1 kWh of electricity" = 1 kWh = 3.6 MJ, the basic unit for household electricity measurement - BTU is primarily used in HVAC (Heating, Ventilation, and Air Conditioning); US cooling equipment is often rated in BTU/h - Food energy values vary greatly: fat 9 kcal/g > protein 4 kcal/g > carbohydrates 4 kcal/g - Law of conservation of energy: Energy cannot be created or destroyed, only transformed from one form to another

Application Scenarios

- Nutrition management: Convert food calories (kcal) to kJ to comply with food labeling regulations
- Electricity bills: Understand the energy meaning of monthly electricity consumption (kWh)
- Fitness and weight loss: Balance exercise calorie burn with dietary intake
- Engineering design: Building energy consumption estimation, solar panel output assessment
- HVAC: BTU and kW cooling/heating capacity conversion

Energy — The Universal Currency of the Universe

Einstein's mass-energy equation E=mc² revealed the equivalence of mass and energy. 1 kilogram of matter fully converted releases about 90 PJ (petajoules) of energy, equivalent to 21 million tons of TNT — this is the source of nuclear weapons' power.

From a broader perspective, energy is the key to understanding the evolution of the universe: the residual heat of the Big Bang (cosmic microwave background radiation) fills all of space; stars convert mass to energy through nuclear fusion to emit light and heat; virtually all energy sources on Earth ultimately come from solar fusion — fossil fuels are ancient biomass storing solar energy, while wind and hydropower come from the sun-driven atmospheric cycle.

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