Example 1
λ = 6e-7 m -> E ≈ 2.07 eV (yellow).
Photon energy from wavelength
Enter wavelength in meters. The calculator divides hc by λ and you get photon energy in J and eV. 600 nm (6e-7 m) is about 2.07 eV. When you know hertz instead of nanometers, open E = h·f.
From frequency: E = h·f. Inverse: λ = hc/E. λ = v/f: wavelength.
Result
Wavelength λ (m). The result shows up here.
How it works
Since E = h·f and in vacuum f = c/λ, you multiply and get E = hc/λ. A shorter wave carries more energy per photon. Red at 700 nm is about 1.77 eV, blue at 450 nm about 2.76 eV. You call both light, but the blue photon is clearly more expensive. h and c are built in: h = 6.62607015e-34 J·s, c = 299792458 m/s.
Type 6e-7, that is 600 nm. E = hc/λ ≈ 3.311e-19 J, or 2.07 eV. Cut the wave in half to 300 nm (3e-7 m) and the energy rises to 4.13 eV, almost twice, because λ is in the denominator. Typical slip: typing 600 instead of 6e-7. Then you are computing a 600 m wave, radio, not yellow light, and the eV collapse to a tiny 2e-9.
This is a vacuum model. In glass, n > 1: frequency stays, λ in the medium shrinks. Photon energy is still h·f, so E from a λ measured in glass without n is only an approximation. Here c is the vacuum value. Wi-Fi at λ = 0.125 m is about 9.9e-6 eV. An X-ray at 1 nm (1e-9 m) goes to 1240 eV.
λ has to be positive. Zero is division by zero. λ follows the header in m or ft. Energy stays in J and eV. The chart of E versus λ falls as 1/λ: longer wave, smaller packet. A comma and a period both parse. 7e-7 (700 nm, red) gives 1.77 eV.
The form needs one field. The calculator example 6e-7 → 2.07 eV. 4.5e-7 (450 nm) → 2.76 eV. If the problem gives f in hertz, go to E = h·f and do not convert to λ by hand.
The inverse is on the neighbouring page: from eV you return to nanometers on λ = hc/E. 2 eV give about 620 nm there. Here you stay with λ in meters.
How to use
- Type wavelength in meters. 600 nm is 6e-7, 450 nm is 4.5e-7, Wi-Fi at 12.5 cm is 0.125. Do not type bare nanometers.
- Compute. 6e-7 gives about 2.07 eV. 3e-7 (300 nm, UV) gives 4.13 eV, almost twice as much, because λ is half as long.
- Check the order. 7e-7 (red) is 1.77 eV. 1e-9 (1 nm) is 1240 eV. If you get 1e-9 eV from “600”, the field holds 600 m.
- h and c are built in. This is a vacuum model: in glass λ is shorter at the same f, so E from λ in a medium without n is an approximation.
- When you know hertz, open E = h·f. When you know eV and want λ back, open λ = hc/E.
Formula
E = h · c / λ
h = 6.62607015×10⁻³⁴ J·s, c = 299792458 m/s. λ > 0.
Letters in E = hc/λ
When you know meters instead of hertz, E = hc/λ. Typing 6e-7 (600 nm) gives about 3.311×10⁻¹⁹ J, or 2.07 eV.
- E
- Photon energy from wavelength. 600 nm is 2.07 eV; 300 nm, half the λ, doubles E to about 4.14 eV.
- h
- The same 6.62607015×10⁻³⁴ J·s, now inside the hc product, not in E = h·f.
- c
- Speed of light 299792458 m/s, built in. Together with h it forms the hc numerator at your λ.
- λ
- Wavelength in meters. 6e-7 is 600 nm; 700 nm sits near 1.77 eV, 450 nm near 2.76 eV.
Real-life examples
Example 2
λ = 4.5e-7 m -> E ≈ 2.76 eV.
Example 3
λ = 7e-7 m -> E ≈ 1.77 eV.
Example 4
λ = 3e-7 m -> E ≈ 4.13 eV.
Example 5
λ = 1e-9 m -> E ≈ 1240 eV.
Example 6
λ = 0.125 m -> E ≈ 9.9e-6 eV.
Example 7
λ = 3 m -> E ≈ 4.1e-7 eV.
Example 8
λ = 1e-8 m -> E ≈ 124 eV.
Ways to use this calculator
- From the nm on an LED package you read photon eV: 600 nm → 2.07 eV.
- You compare red 700 nm (1.77 eV) with UV 300 nm (4.13 eV).
Frequently asked questions
How many eV at λ = 600 nm?
Type 6e-7 m. E ≈ 2.07 eV. 300 nm (3e-7) gives 4.13 eV, almost twice as much.
How do I type nanometers if the field is in meters?
600 nm = 6e-7 m. 450 nm = 4.5e-7. Typing 600 computes a 600 m wave, not light.
Where does hc/λ come from?
From E = h·f and f = c/λ in vacuum. Multiply and you get E = hc/λ. Shorter λ, larger E.
How much at 700 nm and at 450 nm?
700 nm (7e-7) ≈ 1.77 eV, red. 450 nm (4.5e-7) ≈ 2.76 eV, blue.
Is this light in glass or in water?
The model uses vacuum c. In a medium λ is shorter at the same f, so E from λ in glass without n is an approximation.
When should I use E = h·f instead?
When you know f (a spectrometer in Hz, radio). Here you know λ from an LED label or a diffraction grating.
How many eV at λ = 0.125 m?
About 9.9e-6 eV. That is Wi-Fi, not light. 1 nm (1e-9 m) is already 1240 eV.
What if λ = 0?
You would divide by zero. Wavelength must be positive.
Where do I invert this sum?
On λ = hc/E you type energy in eV and get wavelength back. 2 eV ≈ 620 nm.
Can I type my own h or c?
No. They are fixed. If a problem asks for another c, that is usually a medium, not a new constant.
Knowledge sources
The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.
Page updated in 2026.