Quick answer
Photon energy is E = hf = hc ÷ λ. Light of 500 nm has an energy of 3.9729 × 10⁻¹⁹ J, which is 2.4797 eV, at a frequency of 599.58 THz.
Choose whether you know the wavelength or frequency and enter it. The calculator returns energy in joules and electronvolts and the other quantity.
Related tools: Wavelength Calculator: Wavelength from wave speed and frequency. Potential Energy Calculator: Gravitational potential energy from mass, height and gravity. Kinetic Energy Calculator: Kinetic energy and momentum of a moving mass.
How to use the Photon Energy Calculator
- Choose start from: From wavelength (nm) and From frequency (THz).
- Enter wavelength (nm) or frequency (THz) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Start from | Choose one: From wavelength (nm); From frequency (THz) | Starts at From wavelength (nm) |
| Wavelength (nm) or frequency (THz) | A number | > 0 |
Formula and method
Formula
E = h f = h c ÷ λ
IEEE-754 double precision; shown to the decimals indicated.
h = 6.62607015×10⁻³⁴ J·s, c = 299,792,458 m/s, 1 eV = 1.602176634×10⁻¹⁹ J (all exact).
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Start from = From wavelength (nm); Wavelength (nm) or frequency (THz) = 500.
| Result | Value |
|---|---|
| Photon energy | 3.9729e-19 J |
| In electronvolts | 2.4797 eV |
| Wavelength | 500 nm |
| Frequency | 599.5849 THz |
Example 2
Inputs: Start from = From frequency (THz); Wavelength (nm) or frequency (THz) = 600.
| Result | Value |
|---|---|
| Photon energy | 3.9756e-19 J |
| In electronvolts | 2.4814 eV |
| Wavelength | 499.6541 nm |
| Frequency | 600 THz |
Example 3
Inputs: Start from = From wavelength (nm); Wavelength (nm) or frequency (THz) = 121.6.
| Result | Value |
|---|---|
| Photon energy | 1.6336e-18 J |
| In electronvolts | 10.1961 eV |
| Wavelength | 121.6 nm |
| Frequency | 2,465.3985 THz |
The first line is the headline result (photon energy). Below it the photon Energy Calculator lists in electronvolts, wavelength and frequency, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Worked example
f = c ÷ λ = 2.998 × 10⁸ ÷ 500 × 10⁻⁹ = 5.996 × 10¹⁴ Hz. E = 6.626 × 10⁻³⁴ × 5.996 × 10¹⁴ = 3.973 × 10⁻¹⁹ J, or 2.48 eV.
Spectrum
Visible light runs from about 1.65 eV (red, 750 nm) to 3.1 eV (violet, 400 nm). Shorter wavelengths carry more energy per photon. Wavelengths are vacuum wavelengths.
How the result changes with wavelength or frequency
Holding every other input at the first worked example, this table changes only wavelength or frequency. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Wavelength or frequency | Photon energy | In electronvolts | Wavelength |
|---|---|---|---|
| 250 | 7.9458e-19 J | 4.9594 eV | 250 nm |
| 500 | 3.9729e-19 J | 2.4797 eV | 500 nm |
| 1000 | 1.9864e-19 J | 1.2398 eV | 1,000 nm |
| 2000 | 9.9322e-20 J | 0.6199 eV | 2,000 nm |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Wavelength (nm) or frequency (THz): entering "0" shows "Wavelength (nm) or frequency (THz) must be greater than 0." beside that field and no result.
Choosing between the Photon Energy Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Wavelength Calculator](/science/wavelength-calculator/) | wave speed and frequency | Wavelength |
| [Potential Energy Calculator](/science/potential-energy-calculator/) | mass, height and gravitational acceleration | Potential energy |
| [Kinetic Energy Calculator](/science/kinetic-energy-calculator/) | mass and speed | Kinetic energy |
| [Energy Converter](/converters/energy-converter/) | value, from and to | Megawatt-hour (MWh) → Kilowatt-hour (kWh) |
| [Appliance Energy Cost Calculator](/lifestyle/appliance-energy-cost-calculator/) | power, hours used per day and electricity price | Cost per day |
Background: gravity, rotation and optics
Gravity and rotation calculations use a few core relations: a circular orbit has speed v = √(GM ÷ r), torque equals moment of inertia times angular acceleration (τ = Iα), and a thin lens obeys 1/f = 1/dₒ + 1/dᵢ. The moment of inertia depends on both the shape and the axis of rotation.
Use SI units (metres, kilograms, seconds) and check the sign conventions of the formula before interpreting a negative result.
Assumptions and limitations
- Vacuum wavelength
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for wavelength (nm) or frequency (THz) to confirm this.
Frequently asked questions
What is Planck's constant?
Planck's constant is 6.62607015 × 10⁻³⁴ J·s, exact since 2019.
What colour is 500 nm?
500 nm light is green (about blue-green to green), in the middle of the visible spectrum.
How many eV in a joule?
One joule is about 6.242 × 10¹⁸ electronvolts, since 1 eV = 1.602 × 10⁻¹⁹ J.
What does the Photon Energy Calculator calculate?
Photon energy from wavelength or frequency. It returns Photon energy, In electronvolts, Wavelength and Frequency.
What formula does the Photon Energy Calculator use?
E = h f = h c ÷ λ. h = 6.62607015×10⁻³⁴ J·s, c = 299,792,458 m/s, 1 eV = 1.602176634×10⁻¹⁹ J (all exact).
What do I need to enter in the photon Energy Calculator?
You enter Start from and Wavelength (nm) or frequency (THz).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Vacuum wavelength.
What does the “Start from” option change?
It sets how the photon Energy is worked out. The choices are From wavelength (nm) and From frequency (THz).
What is an example of a photon Energy result?
With start from From wavelength (nm) and wavelength (nm) or frequency (THz) 500, the photon energy is 3.9729e-19 J.
Related calculators
- Wavelength Calculator — Wavelength from wave speed and frequency.
- Potential Energy Calculator — Gravitational potential energy from mass, height and gravity.
- Kinetic Energy Calculator — Kinetic energy and momentum of a moving mass.
- Energy Converter — Convert joules, calories, kWh, BTU and more.
- Appliance Energy Cost Calculator — Electricity cost of running an appliance.
- Dew Point Calculator — Dew point from temperature and relative humidity.
Sources
- CODATA 2018 / SI exact constants: g₀ = 9.80665 m/s², c = 299,792,458 m/s, h = 6.62607015×10⁻³⁴ J·s, e = 1.602176634×10⁻¹⁹ C, G = 6.67430×10⁻¹¹ m³/(kg·s²)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.