What's the difference between joules and calories?

Joules are the SI unit for energy (used in physics), while calories measure heat energy (used in nutrition). 1 calorie = 4.184 joules.

How much energy is in a kilowatt-hour?

1 kWh equals 3.6 million joules or 860 kilocalories, roughly the energy used by a 1000W appliance running for 1 hour.

What are food calories?

Food 'Calories' (capital C) are actually kilocalories (kcal), meaning 1 food Calorie = 1000 calories = 4184 joules.

What is a BTU used for?

BTUs (British Thermal Units) measure heating/cooling capacity in HVAC systems and fuel energy content. 1 BTU ≈ 1055 joules.

How are electronvolts used?

Electronvolts (eV) measure tiny energy amounts in atomic and particle physics, like electron binding energies. 1 eV = 1.6×10⁻¹⁹ joules.

Why do we need different energy units?

Different fields use units scaled to their typical values: physics uses joules, nutrition uses kilocalories, electricity uses kWh, making numbers easier to work with.

Can I convert between power and energy?

Power (watts) is energy per time. Energy = Power × Time. For example, 100W for 10 hours = 1000 Wh = 1 kWh.

Conversion Calculators

Energy Converter

Convert between energy units including joules, calories, BTU, kilowatt-hours, and more with precision thermodynamic calculations for engineering, nutrition, and scientific applications. Features both mechanical and thermal energy conversions with detailed explanations.

How to Use the Energy Converter

Use the Energy Converter to between energy units including joules, calories, BTU, kilowatt-hours, and more with precision thermodynamic calculations for engineering, nutrition, and scientific applications. Features both mechanical and thermal energy conversions with detailed explanations.. Enter your values to get accurate, instant results tailored to your situation.

Free unit conversion calculators for length, weight, temperature, volume, and more. Convert between metric and imperial units instantly.

Common Uses

Calculate energy accurately and instantly
Calculate converter accurately and instantly
Calculate convert accurately and instantly
Calculate between accurately and instantly
Calculate energy accurately and instantly

Related Calculators

More Conversion Calculators

Browse all 311+ free online calculators

Energy Unit Guide

Convert between energy units

Expert Tips

Food Calories vs Chemistry calories: Food "Calories" (capital C) are kilocalories. 1 food Calorie = 1000 chemistry calories = 4184 joules.
kWh for Electricity Bills: Kilowatt-hours measure electricity usage. 1 kWh = 3.6 million joules = running 1000W device for 1 hour.
BTUs in HVAC Systems: British Thermal Units measure heating/cooling capacity. 1 BTU = energy to heat 1 pound of water by 1°F = 1055 joules.
Joules: The SI Standard: Joules are the scientific standard for energy. All other units convert to/from joules for universal comparison.

Essential Fundamentals — Common units

Core Energy Units

Joules (J): SI unit for energy. Used in physics and science. 1 joule = force of 1 newton over 1 meter.
Calories (cal): Energy to raise 1 gram of water by 1°C. Used in chemistry and nutrition (as kilocalories).
Kilowatt-hours (kWh): Electrical energy usage. 1 kWh = energy used by 1000W appliance running 1 hour = 3.6 million joules.

Specialized Energy Units

BTU (British Thermal Unit): Used in HVAC systems. 1 BTU = energy to heat 1 pound of water by 1°F = 1055 joules.
Food Calories: Nutritional Calories (capital C) are actually kilocalories. 1 food Calorie = 1000 chemistry calories = 4184 joules.

Advanced Strategies — Practical applications

Real-World Conversions

Utility Bills: Electricity measured in kWh. Natural gas in therms. Compare costs by converting both to joules or BTUs.
Nutrition Labels: Food labels show Calories (kcal). Multiply by 4.184 to get kilojoules, which are used in some countries.

Frequently Asked Questions

What's the difference between joules and calories?: Joules are the SI unit for energy (used in physics), while calories measure heat energy (used in nutrition). 1 calorie = 4.184 joules.
How much energy is in a kilowatt-hour?: 1 kWh equals 3.6 million joules or 860 kilocalories, roughly the energy used by a 1000W appliance running for 1 hour.
What are food calories?: Food 'Calories' (capital C) are actually kilocalories (kcal), meaning 1 food Calorie = 1000 calories = 4184 joules.
What is a BTU used for?: BTUs (British Thermal Units) measure heating/cooling capacity in HVAC systems and fuel energy content. 1 BTU ≈ 1055 joules.
How are electronvolts used?: Electronvolts (eV) measure tiny energy amounts in atomic and particle physics, like electron binding energies. 1 eV = 1.6×10⁻¹⁹ joules.
Why do we need different energy units?: Different fields use units scaled to their typical values: physics uses joules, nutrition uses kilocalories, electricity uses kWh, making numbers easier to work with.
Can I convert between power and energy?: Power (watts) is energy per time. Energy = Power × Time. For example, 100W for 10 hours = 1000 Wh = 1 kWh.