Energy Converter

How to use the energy converter

Choose the unit you have in From and the unit you want in To, type the value and press Convert. Negative values are accepted, because energy figures are often differences, such as the net energy a solar installation exports to the grid in a month.

How energy conversion works

Every unit on this page is a fixed multiple of the joule (J), the SI unit of energy. One joule is the work done by a force of one newton over one meter, and also the energy delivered by one watt in one second. The converter turns your value into joules and then into the target unit, using exact definitions wherever they exist:

• Watt-hour: one watt for 3,600 seconds, so 1 Wh is exactly 3,600 J and 1 kWh is exactly 3.6 MJ.
• Calories: the thermochemical calorie is exactly 4.184 J and the International Table calorie is exactly 4.1868 J. Their kilocalories are 1,000 times larger.
• British thermal unit: the heat that warms one pound of water by one degree Fahrenheit. It is derived here from the International Table calorie, which gives about 1,055.056 J.
• Electronvolt: the energy an electron gains across one volt, exactly 1.602176634 × 10⁻¹⁹ J since the 2019 revision of the SI.

Common energy conversion factors

Multiply a value in the first unit by the factor to get the second unit.

Worked examples

• 350 kWh to MJ (a monthly electricity reading): 350 × 3.6 = 1,260 MJ.
• 2,000 food Calories to kJ: 2,000 × 4.184 = 8,368 kJ, which is about 2.32 kWh.
• 80 US therms to kWh: 80 × 29.3001 ≈ 2,344.01 kWh.
• 1,000,000 Btu to kWh (the "MMBtu" used in natural gas pricing): 1,000,000 × 0.000293071 ≈ 293.07 kWh, or about 1.055 GJ.

Kilowatt-hours to megajoules and Btu

Food Calories to kilojoules

US therms to kilowatt-hours

Energy is not power: kWh versus kW

A kilowatt (kW) is a rate: how fast energy is used or produced. A kilowatt-hour (kWh) is an amount: the energy delivered at one kilowatt for one hour. A 2 kW heater running for 3 hours uses 2 × 3 = 6 kWh. Electricity is billed in kWh because you pay for the amount, while appliances and generators are rated in W or kW. Writing "kW/h" for kWh is a common mistake: kilowatts per hour would be a rate of change of power, not an energy.

This converter cannot turn kW into kWh, because that needs a duration. Multiply the power in kW by the time in hours, or use the power converter to change the power unit first.

Calorie, kilocalorie and the food Calorie

The calorie was first described as the heat needed to warm one gram of water by one degree Celsius. That amount depends slightly on the starting temperature, so two fixed definitions came into use: the thermochemical calorie (4.184 J) and the International Table calorie (4.1868 J). They differ by about 0.067%.

The Calorie on a food label, often written with a capital C or as kcal, is a kilocalorie: 1,000 small calories. In this tool the Food calorie (Cal) is the thermochemical kilocalorie, 4.184 kJ. Converting 250 Cal gives 1,046 kJ; using the International Table kilocalorie instead gives 1,046.7 kJ. The gap is negligible for a meal but explains why published tables sometimes disagree in the last digit.

Btu and therms

Btu are common in North American heating, cooling and gas figures. The tool offers both the International Table Btu (about 1,055.056 J) and the thermochemical Btu (about 1,054.350 J). A therm is roughly 100,000 Btu, but two definitions exist: the US therm is 105.4804 MJ and the EC therm 105.506 MJ, a difference of about 0.024%.

Common pitfalls

• Gas meter volumes are not energy. A meter reading in cubic meters or cubic feet must be multiplied by the calorific value of the gas, which varies with its composition. Suppliers state the value they use; this converter does not include that step.
• Torque looks like energy. Torque is written in N·m or lbf·ft, the same dimensions as the joule and the foot-pound, but it is a different quantity. The numeric factor is the same (1 ft·lbf is about 1.3558 J), yet a torque result should be labelled N·m, not J.
• TNT equivalents are conventions. A ton of TNT is defined as exactly 4.184 GJ, not measured from real explosives.

Frequently asked questions

How many megajoules are in a kilowatt-hour?

Exactly 3.6 MJ, because 1,000 W × 3,600 s = 3,600,000 J.

How many Btu are in a kilowatt-hour?

About 3,412.14 International Table Btu.

How many kilocalories are in a kilowatt-hour?

About 860.42 thermochemical kilocalories, or about 859.85 International Table kilocalories.

Is a Calorie the same as a calorie?

No. A food Calorie is a kilocalorie, 1,000 times a small calorie. Choose Cal or a kcal unit for nutrition figures, and cal only for small laboratory quantities.

What is a horsepower-hour?

The energy delivered by one mechanical horsepower for one hour, about 2.6845 MJ or 0.7457 kWh.

Supported units

• Joule (J)
• Kilojoule (kJ)
• Megajoule (MJ)
• Gigajoule (GJ)
• Millijoule (mJ)
• Watt-hour (Wh)
• Kilowatt-hour (kWh)
• Megawatt-hour (MWh)
• Gigawatt-hour (GWh)
• Food calorie (kilocalorie) (Cal)
• Calorie (thermochemical) (cal (th))
• Kilocalorie (thermochemical) (kcal (th))
• Calorie (International Table) (cal (IT))
• Kilocalorie (International Table) (kcal (IT))
• British thermal unit (IT) (Btu)
• British thermal unit (thermochemical) (Btu (th))
• Therm (US) (thm (US))
• Therm (EC) (thm (EC))
• Electronvolt (eV)
• Kiloelectronvolt (keV)
• Megaelectronvolt (MeV)
• Erg (erg)
• Foot-pound force (ft·lbf)
• Inch-pound force (in·lbf)
• Kilogram-force meter (kgf·m)
• Horsepower-hour (hp·h)
• Ton of TNT (t TNT)
• Kiloton of TNT (kt TNT)
• Megaton of TNT (Mt TNT)