# Energy Converter

Free energy converter. Convert between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, and BTU with exact conversion factors.

## What this calculates

Convert between common energy units including joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, and BTU. All conversions use internationally standardized conversion factors.

## Inputs

- **Value** — min 0
- **From** — options: Joules (J), Kilojoules (kJ), Calories (cal), Kilocalories (kcal), Watt-hours (Wh), Kilowatt-hours (kWh), British Thermal Units (BTU)
- **To** — options: Joules (J), Kilojoules (kJ), Calories (cal), Kilocalories (kcal), Watt-hours (Wh), Kilowatt-hours (kWh), British Thermal Units (BTU)

## Outputs

- **Result** — The converted energy value.
- **Conversion** — formatted as text — Step-by-step conversion explanation.

## Details

Energy conversion spans multiple fields: physics uses joules, nutrition uses kilocalories (often just called 'Calories'), electrical engineering uses watt-hours, and HVAC systems use BTU.

Key Conversion Factors

- 1 thermochemical calorie = 4.184 joules (exact, by definition)

- 1 kilocalorie (food Calorie) = 4,184 joules

- 1 watt-hour = 3,600 joules (exact)

- 1 kilowatt-hour = 3,600,000 joules (exact)

- 1 BTU (International Table) = 1,055.056 joules

- 1 kWh = 3,412.14 BTU

- 1 kWh = 860.421 kcal

Practical Context

- A food Calorie (kcal) can raise 1 kg of water by 1°C

- A 100W light bulb uses 0.1 kWh per hour

- Heating a typical US home for a day uses roughly 100,000 BTU

## Frequently Asked Questions

**Q: How do I convert calories to joules?**

A: Multiply the number of calories by 4.184 to get joules. This is the exact thermochemical calorie definition. For example, 500 cal = 500 × 4.184 = 2,092 J. Note: food 'Calories' (capital C) are actually kilocalories (1 Cal = 1 kcal = 4,184 J).

**Q: What is the difference between a calorie and a Calorie?**

A: A small calorie (cal) is the energy needed to raise 1 gram of water by 1°C. A large Calorie or food Calorie (Cal) is actually 1 kilocalorie (kcal) = 1,000 small calories. Food labels use Calories (kcal). When nutrition says '2,000 Calories per day,' it means 2,000 kcal.

**Q: How many BTU are in a kilowatt-hour?**

A: One kilowatt-hour equals approximately 3,412.14 BTU. This conversion is important for HVAC systems, which are typically rated in BTU, while electricity is billed in kWh. To convert kWh to BTU, multiply by 3,412.14.

**Q: What is a BTU?**

A: A British Thermal Unit (BTU) is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. The International Table BTU is exactly 1,055.05585262 joules. BTUs are commonly used in heating, cooling, and energy industries.

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Source: https://vastcalc.com/calculators/conversion/energy-converter
Category: Conversion
Last updated: 2026-04-21