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Energy Converter

Converts energy between joules (J to GJ), calories (thermochemical cal = 4.184 J, kcal), watt-hours (Wh, kWh, MWh), BTU (International Table, 1055.05585262 J), MMBTU, therm (EC), electronvolts, ergs and foot-pounds.

ValueAmount to convert, expressed in from_unit. From unitUnit of the input value. Accepted symbols: J, kJ, MJ, GJ, erg, cal, kcal, Wh, kWh, MWh, BTU, MMBTU, therm, eV, ft_lbf; spelled-out names and common abbreviations are accepted too. To unitUnit to convert into (same symbols as from_unit).

When to use

You need an energy amount in another unit, e.g. kWh to MJ, kcal to kJ, BTU to kWh or therms to kWh for utility bills.

Do not use when: You need power (rate of energy, use power), the cost of electricity (use electricity-cost) or calories from macronutrient grams (use calories-from-macros).

Formula

result = value × factor, factor = (1 from_unit in J) / (1 to_unit in J)

cal is the thermochemical calorie (4.184 J) and kcal the food Calorie (4184 J); BTU is the International Table BTU and therm the EC therm (100,000 BTU_IT). The International Steam Table calorie (4.1868 J) and US therm (105,480,400 J) differ by 0.07% and 0.02%.

Inputs

Parameter	Type	Required	Description
`value`	number	yes	Amount to convert, expressed in from_unit.
`from_unit`	enum: J \| kJ \| MJ \| GJ \| erg \| cal \| kcal \| Wh \| kWh \| MWh \| BTU \| MMBTU \| therm \| eV \| ft_lbf	yes	Unit of the input value. Accepted symbols: J, kJ, MJ, GJ, erg, cal, kcal, Wh, kWh, MWh, BTU, MMBTU, therm, eV, ft_lbf; spelled-out names and common abbreviations are accepted too.
`to_unit`	enum: J \| kJ \| MJ \| GJ \| erg \| cal \| kcal \| Wh \| kWh \| MWh \| BTU \| MMBTU \| therm \| eV \| ft_lbf	yes	Unit to convert into (same symbols as from_unit).

Outputs

Output	Type	Description
`result`	number	Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).
`result_text`	string	The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km".
`formula`	string	Relation used, e.g. "1 mi = 1.609344 km".
`factor`	number	Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.
`conversion_table`	object	The input value expressed in every supported energy unit (6 significant figures), keyed by unit symbol.

Example

100 kWh to megajoules: {"value":100,"from_unit":"kWh","to_unit":"MJ"} → {"result":360,"factor":3.6,"formula":"1 kWh = 3.6 MJ","conversion_table":{"BTU":341214,"kcal":86042.1}}

2000 kcal to kilojoules: {"value":2000,"from_unit":"kcal","to_unit":"kJ"} → {"result":8368,"factor":4.184,"conversion_table":{"kWh":2.32444,"BTU":7931.34}}

GET https://tttkmbb.com/api/v1/calculate/energy?value=100&from_unit=kWh&to_unit=MJ

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/energy (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/energy · Markdown: https://tttkmbb.com/conversion/energy.md · JSON definition: https://tttkmbb.com/conversion/energy.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="energy"
OpenAPI operationId: convert_energy
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Is a food Calorie the same as a calorie?

A food Calorie (kcal, 'large calorie') is 1000 thermochemical calories (cal). Use kcal for nutrition labels.

Which BTU is used?

The International Table BTU (1055.05585262 J), the definition used by NIST SP 811 and in HVAC ratings. The thermochemical BTU (1054.35 J) is 0.07% smaller.

How many kWh in a therm?

29.3071 kWh (1 therm = 100,000 BTU = 105.5056 MJ).

Related calculators

Power Converter — Energy per unit time (W, hp, BTU/h).
Electricity Cost Calculator — Cost of a kWh amount at a tariff.
Kinetic Energy Calculator — Energy of a moving mass in joules.