What this calculator does
The Energy Unit Conversion Calculator turns a single energy value into its equivalent across twelve common units at once: erg, joule (J), kilowatt-hour (kWh), thermochemical and International Table calories and kilocalories (cal_th, kcal_th, cal_IT, kcal_IT), electronvolt (eV), the IT British thermal unit (BTU), foot pound-force (ft.lbf), foot poundal (ft.pdl) and litre-atmosphere (L.atm). Energy is a universal physical quantity, so these conversions apply identically everywhere in the world.
How to use it
Type your number in the Energy box, pick the Unit that the number is expressed in, and optionally choose how many significant digits to display. The calculator immediately fills the table with the same energy written in every other unit.
The formula explained
Every unit has a fixed conversion factor giving how many joules equal one of that unit. The tool first normalises your input to the SI base unit, the joule, using $$E_{\text{J}} = E_{\text{input}} \times f_{\text{input}}$$ It then converts to each target unit with $$E_{\text{target}} = \frac{E_{\text{J}}}{f_{\text{target}}}$$ Key factors include \(1\ \text{kWh} = 3{,}600{,}000\ \text{J}\), \(1\ \text{cal\_th} = 4.184\ \text{J}\), \(1\ \text{cal\_IT} = 4.1868\ \text{J}\), \(1\ \text{BTU (IT)} = 1055.05585262\ \text{J}\), \(1\ \text{eV} = 1.602176634 \times 10^{-19}\ \text{J}\) and \(1\ \text{L.atm} = 101.325\ \text{J}\).
Worked example
Enter 1 in the Energy box and select joule. The result table shows \(10{,}000{,}000\) erg, \(2.7778 \times 10^{-7}\) kWh, \(0.23901\) cal_th, \(0.23885\) cal_IT, about \(6.24 \times 10^{18}\) eV, \(9.4782 \times 10^{-4}\) BTU, \(0.73756\) ft.lbf, \(23.730\) ft.pdl and \(9.8692 \times 10^{-3}\) L.atm. Enter 2 kWh and the calculator reports \(7{,}200{,}000\) J and about \(1719.69\) kcal_IT.
FAQ
What is the difference between a thermochemical and an IT calorie? The thermochemical calorie is defined as exactly 4.184 J, while the International Table calorie is 4.1868 J. Both are offered so you can match whichever standard your source uses.
Which BTU is used? The International Table BTU of 1055.05585262 J, the most common definition. The thermochemical BTU (1054.35 J) differs slightly.
Can I enter negative or scientific-notation values? Yes. The sign passes through unchanged, and very large or small results are shown so you can read tiny or huge conversions such as electronvolts.
