Our free energy converter does all energy conversion by one click. Enter a value, pick your units, and see the answer instantly, along with every other unit at once.
Energy Converter
Convert any energy unit instantly, including nm to eV.
All units
Power to energy
How to Use the Energy Converter
- Type your value in the Value box.
- Choose the unit you have in From.
- Choose the unit you want in To.
- Read the result instantly. Press the swap button to flip the units.
The table below the result shows your value in all other units at the same time, so you can compare without repeating the steps.
Energy Converter Units
Our tool supports the units people use most:
- Joule (J), kilojoule (kJ), megajoule (MJ), gigajoule (GJ): the SI (metric) family used in science and engineering.
- Watt-hour (Wh), kilowatt-hour (kWh), megawatt-hour (MWh): electricity billing and battery capacity.
- Calorie (cal) and kilocalorie (kcal): food energy. The “Calories” on a nutrition label are actually kilocalories.
- BTU and therm: heating, air conditioning, and natural gas in the United States.
- Foot-pound (ft·lbf) and horsepower-hour: mechanical work.
- Electronvolt (eV), keV, MeV: atoms, semiconductors, and particle physics.
- Ton of oil equivalent (toe) and ton of TNT: large-scale energy and explosives comparisons.
- Erg: an older, very small metric unit still found in physics texts.
Energy Unit Conversion Table
| Unit | Equals in Joules (J) |
|---|---|
| 1 kilojoule (kJ) | 1,000 J |
| 1 watt-hour (Wh) | 3,600 J |
| 1 kilowatt-hour (kWh) | 3,600,000 J |
| 1 calorie (cal) | 4.184 J |
| 1 kilocalorie (kcal) | 4,184 J |
| 1 BTU (IT) | 1,055.06 J |
| 1 therm | 105,480,400 J |
| 1 foot-pound (ft·lbf) | 1.3558 J |
| 1 horsepower-hour | 2,684,520 J |
| 1 erg | 0.0000001 J |
| 1 electronvolt (eV) | 1.602 × 10⁻¹⁹ J |
Handy shortcuts: multiply kWh by 3.6 to get megajoules. Multiply kcal by 4.184 to get kilojoules. Divide BTU by 3,412 to get kWh.
Energy Converter nm to eV
Light is made of photons, and each photon carries energy that depends on its wavelength. Shorter wavelengths carry more energy. To convert nanometers (nm) to electronvolts (eV), use this formula:
E (eV) = 1239.84 ÷ wavelength (nm)
The number 1239.84 comes from Planck’s constant multiplied by the speed of light, divided by the charge of an electron. Many textbooks round it to 1240. For research and device design, use the more precise value, which is what our converter does.
To go the other way, divide 1239.84 by the energy in eV to get the wavelength in nm.
Example: green light at 500 nm has an energy of 1239.84 ÷ 500 = 2.48 eV.
| Wavelength | Energy | Region |
|---|---|---|
| 200 nm | 6.20 eV | Ultraviolet |
| 400 nm | 3.10 eV | Violet |
| 500 nm | 2.48 eV | Green |
| 589 nm | 2.10 eV | Sodium yellow |
| 700 nm | 1.77 eV | Red |
| 1000 nm | 1.24 eV | Near infrared |
To use this in the tool, choose “Wavelength (nm) to photon energy” as one unit and eV as the other.
How Can I Convert Power to Energy?
Power and energy are not the same thing. Power is how fast energy is used, measured in watts. Energy is the total amount used over time. The link between them is simple:
Energy = Power × Time
To find kilowatt-hours, multiply watts by hours and divide by 1,000.
Example 1: a 100-watt bulb running for 5 hours uses 100 × 5 = 500 Wh, which is 0.5 kWh, or 1,800,000 joules.
Example 2: a 2 kW heater running for 3 hours uses 2 × 3 = 6 kWh.
If your time is in minutes, divide by 60 first. To estimate cost, multiply your kWh by the price per kWh on your utility bill. The power-to-energy box in the tool above does this for you.
Frequently Asked Questions
How many joules are in a kilowatt-hour?
One kilowatt-hour equals exactly 3,600,000 joules, or 3.6 megajoules.
How do I convert joules to calories?
Divide joules by 4.184 to get calories. For example, 1,000 J ÷ 4.184 is about 239 cal.
Are food Calories the same as calories?
No. A food Calorie (capital C) is a kilocalorie, which equals 1,000 small calories or 4,184 joules.
What is an electronvolt?
An electronvolt is the energy an electron gains when it moves through one volt. It equals about 1.602 × 10⁻¹⁹ joules and is used for atomic and photon energies.
Is the energy converter free?
Yes. It is free, needs no sign-up, and works on phones, tablets, and computers.
What is the difference between kW and kWh?
A kW measures power, or how fast energy is used. A kWh measures energy, or how much was used. A 1 kW appliance running for one hour uses 1 kWh.
How accurate is the converter?
It uses standard international conversion factors, including the exact definition of the electronvolt, so results are reliable for school, work, and everyday use.
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Whether you are checking a power bill, planning a diet, sizing a heater, or working through a physics problem, the energy converter above gives you a fast, accurate answer. Bookmark this page and come back any time you need to switch between energy units.