Home/Tools/Energy, power & force
Electronvolts to Joules Converter
1 eV = 1.602176634 × 10⁻¹⁹ J exactly.
—
An exact figure, since 2019
An electronvolt is the energy an electron picks up crossing a potential difference of one volt. That makes the conversion factor equal to the elementary charge in coulombs.
1 eV = 1.602176634 × 10−19 J exactly
Until 2019 this was a measured quantity with an uncertainty attached. The SI redefinition fixed the elementary charge as a defined constant, so the number is now exact by definition and will not change.
The unit exists because joules are hopelessly large for particle physics. A visible photon carries around 2 eV; a chemical bond a few; an X-ray thousands. Writing those in joules means carrying nineteen decimal places.
The electronvolt
The energy an electron gains crossing a potential difference of one volt. Since the 2019 redefinition of SI it is exactly 1.602176634 × 10−19 joules, because the elementary charge is now a defined constant.
It is the natural unit for atomic and particle physics. Visible light photons carry 1.6 to 3.3 eV; chemical bonds are a few eV; particle accelerators work in giga- and tera-electronvolts.
The joule
The SI unit of energy: the work done when a force of one newton moves something one metre. It is a small unit — lifting an apple a metre off the table takes about one joule.
Everything else on this page is the same quantity counted differently. A joule is also one watt for one second, which is the link between energy and power.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where this comes up
- Food labels. Europe and Australia print kilojoules; the United States prints Calories. The same packet often carries both.
- Nutrition and exercise tracking, where one app reports kJ and another kcal.
- Chemistry and physics coursework, where reaction enthalpies come in kJ/mol and older texts use calories.
- Physics at atomic scale, where electronvolts are the only sensible size.
The trap: calorie and Calorie
The word means two things a thousand apart.
- calorie (small c) — the scientific unit, exactly 4.184 joules. Enough to warm a gram of water by one degree.
- Calorie (capital C), or kcal — a thousand of those, 4,184 joules. This is what every food label means.
So a 2,000-Calorie daily intake is 2,000 kcal, which is 2,000,000 small calories, or 8.37 megajoules. If a conversion comes out a thousand away from what you expected, this is why.
Tips worth knowing
- 4.184 is the number to remember. It works at every scale: cal to J, kcal to kJ, Mcal to MJ.
- Energy is not power. Joules are an amount; watts are a rate. They cannot be converted without a time.
- A kilowatt-hour is energy, not power: 3.6 MJ, or 860 kcal.
Values people look up most
Each one opens the converter with the number already in it.
- 1 eV to J
- 1.5 eV to J
- 2 eV to J
- 3 eV to J
- 5 eV to J
- 10 eV to J
- 13.6 eV to J
- 100 eV to J
- 511,000 eV to J
- 1,000 eV to J
- 10,000 eV to J
- 1,000,000 eV to J
- 1,000,000,000 eV to J
Quick reference
13.6 eV is the ionisation energy of hydrogen.
| Electronvolts | Joules |
|---|---|
| 1 eV | 0 J |
| 2 eV | 0 J |
| 13.6 eV | 0 J |
| 1,000 eV | 0 J |
| 100,000 eV | 0 J |
| 1,000,000 eV | 0 J |
| 1,000,000,000 eV | 0 J |
Questions people ask
How many joules in an electronvolt?
1.602176634 × 10⁻¹⁹ J, exactly.
Why is the factor exact now?
Because the 2019 SI redefinition fixed the elementary charge as a defined constant rather than a measured one.
What is 1 keV in joules?
1.602 × 10⁻¹⁶ J. The prefixes work normally: keV, MeV, GeV, TeV.