# Energy converter

> How much is that energy in other units? Convert between joules, kilowatt-hours, kilocalories, BTU and more, using exact definitions.

Energy converter: joules, kJ, MJ, watt-hours, kWh, calories, kcal, BTU and electronvolts, using exact definitions for each conversion.

- Page: https://how.box/conversion/energy/
- Runs entirely in the browser.

## Inputs

Answer link: https://how.box/conversion/energy/?v={v}&from={from}&to={to}

- `v` (number 0 to 1e15): The energy to convert, in the from unit. Example: `1`.
- `from` (j, kj, wh, kwh, mj, cal, kcal, btu or ev): Unit of v (unit id: j, kj, wh, kwh, mj, cal, kcal, btu, ev). Example: `kwh`.
- `to` (j, kj, wh, kwh, mj, cal, kcal, btu or ev): Unit to convert to (unit id). Example: `mj`.

Example answer: https://how.box/conversion/energy/?v=1&from=kwh&to=mj

A complete link carries the primary answer in the page HTML; a missing or invalid value shows the default page.

## Agent tools

- `energy_convert`: Converts an energy between units using exact definitions (1 Wh = 3600 J, 1 kWh = 3.6 MJ, thermochemical calorie 4.184 J so 1 kcal = 4.184 kJ, International Table BTU 1055.05585262 J, 1 eV = 1.602176634e-19 J; BIPM SI Brochure, NIST SP 811 B.8).
  - MCP, one POST to https://how.box/mcp: `{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"energy_convert","arguments":{"value":1,"from_unit":"kwh","to_unit":"mj"}}}`
  - GET: https://how.box/mcp/run/energy_convert?value=1&from_unit=kwh&to_unit=mj

## How it works

Every unit is converted through joules using exact definitions: a watt-hour is 3,600 J (one watt for one hour), a kilowatt-hour is 3.6 million J, a food calorie (kilocalorie) is exactly 4,184 J, and a British thermal unit is about 1,055 J. So a 2,000 kcal day is about 8,368 kJ, and 1 kWh is about 860 kcal.

The joule, watt-hour and electronvolt come from the BIPM SI Brochure; the calorie and BTU definitions from NIST Special Publication 811. Food labels in the EU give energy in kJ and kcal with 1 kcal = 4.184 kJ.

Calories come in several versions. This converter uses the thermochemical calorie (4.184 J) used on food labels, and the International Table BTU.

## FAQ

**How many joules are in a kilowatt-hour?**
Exactly 3,600,000 J, or 3.6 MJ. It is the energy of 1,000 watts running for one hour.

**How many kilojoules are in a calorie?**
A kilocalorie (the “calorie” on food labels) is exactly 4.184 kJ. A small calorie (cal) is 4.184 J.

**How many kWh is a BTU?**
About 0.000293 kWh: 1 kWh is about 3,412 BTU.

**Is energy the same as power?**
No. Energy is the amount (kWh, J). Power is how fast it is used (kW, W). A 1 kW heater running for 2 hours uses 2 kWh.

**Can I convert battery mAh to kWh here?**
Not directly. mAh measures electric charge; energy also needs the voltage. Multiply mAh by nominal volts and divide by 1,000,000 to get kWh.

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