Photon Energy Calculator
Convert between a photon's wavelength, frequency, and single-photon energy using the exact SI values of the Planck constant, speed of light, and elementary charge.
Photon quantities
Edit any one quantity. The other two update from the same physical state.
Required when wavelength is the quantity you edit. Positive decimal or scientific notation.
Required when frequency is the quantity you edit. Frequency must be greater than zero.
Required when energy is the quantity you edit. Energy refers to one photon.
Live result
All displayed quantities describe the same photon in vacuum.
Photon energy
2.38431 eV
Single-photon energy in the selected energy unit.
Current conversion
Canonical SI values and the selected display units are calculated from one model.
| Quantity | Canonical SI value | Selected display |
|---|---|---|
| Wavelength | 5.20000e – 7 m | 520 nm |
| Frequency | 5.76524e14 Hz | 576.524 THz |
| Photon energy | 3.82009e – 19 J | 2.38431 eV |
How to use this photon energy calculator
What this calculator does
This calculator links three equivalent descriptions of a single photon in vacuum: Wavelength, Frequency, and Energy. It applies the Planck – Einstein relation and the vacuum wave relation, so changing any one of the three quantities determines the other two. It is useful for unit conversion and physics checks, but it does not model how light slows in a material, how many photons are present, optical power, absorption probability, or a material's response to radiation.
The calculation uses the exact SI value of the Planck constant. NIST explains why the Planck constant connects a photon's frequency with its energy. The vacuum wavelength-frequency conversion uses the exact speed of light, and electronvolt conversion uses the exact elementary charge.
When to use it
- Convert a laser or LED wavelength into frequency and single-photon energy.
- Translate an X-ray or gamma-ray energy in eV, keV, or MeV into an equivalent frequency or wavelength.
- Check spectroscopy homework, lab calculations, or instrument settings when one photon quantity is known.
- Compare how moving toward shorter wavelengths raises photon energy, or how lower frequencies reduce it.
How to calculate
- The calculator opens with a complete demonstration: 520 nm. That state already produces finite results and a validated example workbook, so Download Excel is available immediately.
- Edit the value under Wavelength, Frequency, or Energy. The most recently edited quantity becomes the source. Use its adjacent unit selector to choose the unit you actually mean.
- Read Photon energy as the primary result. The supporting cards show Wavelength, Frequency, and Energy in joules. The Current conversion table gives the same state in canonical SI units and in your selected display units.
- Select Download Excel to export the current validated values into a real XLSX workbook containing Summary, Inputs, Conversion, and Notes sheets.
- Select Reset to clear the demonstration and all calculated content. Reset does not restore 520 nm; it leaves the data fields empty and may disable Download Excel until you enter a new complete positive value.
Input guide
Wavelength is a positive decimal or scientific-notation value representing the photon's vacuum wavelength. It becomes required when you edit that field. Supported units are m, cm, mm, µm, nm, and pm. A realistic optical example is 520 nm. Increasing wavelength lowers both frequency and photon energy; decreasing it raises them. Do not enter a negative value, zero, a unit symbol inside the value box, or a decimal-comma form such as “1,5”, which is intentionally rejected as ambiguous. Wavelength unit changes the displayed unit and converts the current value without changing the photon.
Frequency is a positive decimal or scientific-notation value in Hz, kHz, MHz, GHz, THz, or PHz. It becomes required when you edit that field. For the demonstration photon, the corresponding value is about 576.524 THz. Higher frequency means proportionally higher energy and a shorter wavelength. A common mistake is confusing hertz with radians per second; this calculator expects ordinary frequency in cycles per second, not angular frequency. Frequency unit converts the current frequency representation while preserving the same physical state.
Energy is the energy of one photon, entered as a positive decimal or scientific-notation value. Choose J, mJ, µJ, nJ, pJ, eV, keV, MeV, or GeV with Energy unit. The demonstration is about 2.38431 eV. Higher energy raises frequency and shortens wavelength. Do not confuse single-photon energy with total beam energy or power; multiplying by a photon count or photon rate is a separate calculation. The NIST elementary charge value defines the exact joule-to-electronvolt conversion used here.
Output guide
Photon energy is the primary single-photon energy shown in the currently selected energy unit. It is an exact identity from the entered photon state, subject only to display rounding. A larger value indicates a higher-frequency, shorter-wavelength photon. Wavelength and Frequency repeat the corresponding values in your selected display units so that all three representations stay visible together. Energy in joules always shows the canonical SI energy in J, which is useful when inserting the result into other SI equations.
The three header pills – Wavelength, Frequency, and Energy – are compact copies of those same canonical model values; they are not separate calculations. In the Current conversion table, the Quantity column names the physical variable, Canonical SI value reports wavelength in meters, frequency in hertz, and energy in joules, and Selected display reports the same quantities using the three unit selectors. Because all values represent one photon, a zero or negative physical value is outside this calculator's valid domain rather than a meaningful result.
Worked example
Start with the demonstration wavelength, λ = 520 nm = 5.20 × 10 – 7 m. Using the exact vacuum speed of light, c = 299,792,458 m/s, the frequency is f = c/λ = 5.7652395769 × 1014 Hz, or 576.524 THz after display rounding. Then apply E = h × f with h = 6.62607015 × 10 – 34 J·s. The result is E = 3.8200881868 × 10 – 19 J. Dividing by the exact joule value of one electronvolt gives 2.38431 eV, matching the calculator's first-open result and its workbook checkpoints.
Learn more
The wavelength-frequency step assumes vacuum propagation. NIST lists the speed of light in vacuum as exactly 299,792,458 m/s. In a material, wavelength changes according to the medium's refractive properties while frequency remains set by the source, so use material-specific optics when that distinction matters.
Formula and interpretation
Photon energy scales linearly with frequency and inversely with wavelength. That means doubling frequency doubles the energy of each photon, while doubling wavelength halves it. This is why ultraviolet, X-ray, and gamma-ray photons sit at progressively higher single-photon energies than visible or radio-frequency photons.
Electronvolts are convenient for atomic and optical scales because joules are very small for individual photons. The calculator nevertheless keeps joules as the canonical energy internally, then converts to the selected unit only for presentation and export. This avoids mixing unit conversions into the underlying physics formula.
Common mistakes
Keep the distinction between wavelength in vacuum and wavelength in a medium, between ordinary frequency and angular frequency, and between energy per photon and total energy delivered by a light source. Also pay attention to prefixes: nm means 10 – 9 m, THz means 1012 Hz, and keV means 103 eV. A prefix error can shift the answer by many orders of magnitude even when the equation itself is correct.