Energy Conversion Calculator

All conversions use the joule as the intermediate reference. The input value is first converted to joules, then from joules to every other unit. The exact conversion factors are:

$$1\;\text{kJ} = 1000\;\text{J}$$

$$1\;\text{cal} = 4.184\;\text{J}$$ (thermochemical calorie, exact by definition)

$$1\;\text{kcal} = 4184\;\text{J}$$

$$1\;\text{eV} = 1.602176634 \times 10^{-19}\;\text{J}$$ (exact, SI 2019)

$$1\;\text{kWh} = 3.6 \times 10^6\;\text{J}$$ (exact)

$$1\;\text{BTU} = 1055.06\;\text{J}$$ (International Table BTU)

$$1\;\text{erg} = 10^{-7}\;\text{J}$$ (CGS unit, exact)

Context for each unit:

• Joule (J): The SI standard. Named after James Prescott Joule. One joule is the work done by a force of one newton over one meter.
• Calorie (cal): Originally the energy to raise 1 g of water by 1 °C. The thermochemical calorie (4.184 J) is used in chemistry; the "food Calorie" is actually a kilocalorie.
• Electronvolt (eV): The energy gained by an electron accelerated through 1 volt. Standard in particle physics, atomic physics, and semiconductor physics. Typical scales: chemical bonds ~1–5 eV, X-rays ~keV, nuclear reactions ~MeV, cosmic rays ~TeV.
• Kilowatt-hour (kWh): The commercial energy unit for electricity billing. 1 kWh = 3.6 MJ = the energy consumed by a 1000 W appliance running for one hour.
• BTU: British Thermal Unit, used in HVAC, heating, and the US energy industry. Approximately the energy to heat 1 pound of water by 1 °F.
• Erg: The CGS unit of energy, still used in astrophysics and some older literature. Very small: 1 erg = 100 nJ.

All eight output values represent the same physical quantity of energy expressed in different units. Use joules for physics calculations, eV for atomic/particle physics, kcal for nutrition and chemistry, kWh for electrical energy, and BTU for heating/cooling applications. The conversion is exact for units with defined conversion factors (kJ, cal, eV, kWh, erg) and precise to 5+ significant figures for BTU.