Example 1
Yellow, f = 5e14 Hz -> E ≈ 2.07 eV.
Photon energy calculator
Enter frequency. The calculator multiplies it by Planck’s constant and you get the energy of one photon in joules and in eV. Yellow 5e14 Hz is about 2.07 eV. When you know nanometers instead of hertz, open E = hc/λ.
From wavelength: E = hc/λ. Inverse: λ = hc/E. Wavelength: λ = v/f.
Result
Frequency f (Hz). The result shows up here.
How it works
Light and radio are waves, but the energy arrives in packets. One packet, a photon, has E = h·f. h = 6.62607015e-34 J·s is fixed; you do not type it. Higher frequency means more energy per photon, not brighter light and not louder radio. Brightness is how many photons per second, a different sum.
Take yellow light from a problem, f = 5e14 Hz. E = h·f = 3.313e-19 J. A joule is too large for one photon, so you divide by 1.602176634e-19 J/eV and get 2.07 eV. Ultraviolet at 1e15 Hz is already 4.14 eV, twice as much, because f is twice as high. X-rays at 3e17 Hz reach 1240 eV, or 1.24 keV.
Radio and microwaves sit many orders lower. Wi-Fi at 2.4 GHz is about 9.9e-6 eV. A 2.45 GHz oven is about 1.0e-5 eV. FM at 100 MHz is about 4.1e-7 eV. Same formula, different shelf. A 440 Hz fork would formally give 1.8e-12 eV, but sound is not a photon: it is a wave in air, with no h in that sense.
f has to be positive. c does not enter E = h·f. The speed of light appears only when you start from wavelength: E = hc/λ, because in vacuum f = c/λ. Hertz does not follow the US header. Energy stays in J and eV. The chart of E versus f is a straight line through the origin.
The form needs one field. Type 5e14 and read 2.07 eV. 1e15 gives 4.14 eV. 2.45e9 gives order 1e-5 eV. A comma and a period both parse. If the problem gives T, get f = 1/T first, then come back here.
When you know λ in nanometers, open E = hc/λ and type meters (600 nm is 6e-7). When you know eV and want λ back, open λ = hc/E. Here you stay with frequency.
How to use
- Type frequency in hertz. Visible light is around 4e14 to 8e14. Yellow in problems is often 5e14.
- Compute. 5e14 gives about 2.07 eV and 3.31e-19 J. The second result is in eV, because a joule is too large for one photon.
- Compare scale. 1e15 Hz (UV) is 4.14 eV. 2.45e9 Hz (oven) is about 1.0e-5 eV, same formula, different shelf.
- If the problem gives period T, get f = 1/T first, then come back. h is built in; you do not type the constant.
- When you know nanometers instead of hertz, open E = hc/λ. When you know eV and want λ, open λ = hc/E.
Formula
E = h · f
h = 6.62607015×10⁻³⁴ J·s (fixed). 1 eV = 1.602176634×10⁻¹⁹ J. f > 0.
Letters in E = h·f
One photon carries E = h·f. Yellow 5×10¹⁴ Hz times h is 3.313×10⁻¹⁹ J, about 2.07 eV.
- E
- Energy of one photon. At f = 5×10¹⁴ Hz that is 3.313×10⁻¹⁹ J, or about 2.07 eV, not the beam brightness.
- h
- Planck constant 6.62607015×10⁻³⁴ J·s, built in. You do not type h; the calculator multiplies your f by it.
- f
- Frequency in hertz. 5×10¹⁴ Hz is this yellow example; nanometers live on E = hc/λ.
Real-life examples
Example 2
f = 5.6e14 Hz -> E ≈ 2.32 eV.
Example 3
f = 1e15 Hz -> E ≈ 4.14 eV.
Example 4
f = 2.45e9 Hz -> E ≈ 1.0e-5 eV.
Example 5
f = 2.4e9 Hz -> E ≈ 9.9e-6 eV.
Example 6
f = 1e8 Hz -> E ≈ 4.1e-7 eV.
Example 7
f = 3e17 Hz -> E ≈ 1240 eV.
Example 8
f = 440 Hz -> E ≈ 1.8e-12 eV (sound, not a photon).
Ways to use this calculator
- You compare 2.07 eV of yellow light with 4.14 eV at 1e15 Hz.
- You type 2.45e9 Hz from a microwave oven and see how much weaker that photon is than light.
Frequently asked questions
How many eV at f = 5e14 Hz?
E = h·f ≈ 3.313e-19 J, or 2.07 eV. That is yellow light from many problems.
What value is h, and can I change it?
h = 6.62607015e-34 J·s. It is fixed in the calculator. Same h as in E = hc/λ.
Why is there a second result in eV?
A joule is too large for one visible photon. 1 eV = 1.602176634e-19 J, so yellow comes out near 2 eV.
How much at f = 1e15 Hz?
E ≈ 4.14 eV. Twice the f of 5e14, twice the energy per photon.
Does E = h·f work for sound from a speaker?
No. Sound is a mechanical wave in air. E = h·f is for EM radiation: radio, light, X-rays.
How do I go from f to wavelength?
In vacuum λ = c/f, then E = hc/λ. Or open E = hc/λ directly when you know λ instead of f.
How many eV is a 2.4 GHz Wi-Fi photon?
About 9.9e-6 eV. A 2.45 GHz oven is about 1.0e-5 eV. Many orders below light.
Does the speed of light enter E = h·f?
No. c appears when you start from λ: E = hc/λ. Here you know f, so h is enough.
Where is the photon count or laser power?
Here you compute the energy of one photon. Beam power is N·E / time; that field is not here, because it is a different sum.
How much at f = 3e17 Hz?
E ≈ 1240 eV, or 1.24 keV. That is already soft X-ray, not a light bulb.
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.