Do I have to change c when the wave is in a medium?

Yes, if you want the in-medium wavelength. The relation c = λ·f uses the wave's actual speed, and light slows to c/n inside a medium (n = refractive index). Switch the wave-speed control to "refractive index" and enter n — water is about 1.33, common glass about 1.5 — and the calculator uses c/n. Crucially the frequency does not change when light crosses into a medium; only the wavelength shrinks. That is why this tool always computes photon energy from the frequency (E = h·f) and always classifies the spectrum band from the vacuum wavelength, so a glass or water value is not mislabelled.

How do I convert between eV and joules?

One electronvolt is the energy an electron gains crossing a 1-volt potential: 1 eV = 1.602 176 634 × 10⁻¹⁹ J (the elementary charge, CODATA exact). To go from joules to eV, divide by that number; to go the other way, multiply. The energy unit toggle does it for you — switch between J and eV and the displayed value updates without touching anything else. As a sanity check, a visible-light photon sits in the 1.6–3.3 eV range, which is why semiconductor band gaps are quoted in eV.

What is the wavelength range of visible light?

This calculator treats roughly 380–700 nm as visible, the conventional optics window. Inside it the tool also names an approximate colour: violet near 380–450 nm, blue 450–485, cyan 485–500, green 500–565, yellow 565–590, orange 590–625, and red 625–700. The edges are deliberately fuzzy — human colour perception varies and sources quote 380–740 nm or 400–700 nm — so treat the colour as a guide, not a hard boundary. Below 380 nm you are in the ultraviolet; above 700 nm, the infrared.

Does a higher frequency always mean more energy?

For a single photon, yes — E = h·f is strictly proportional, so doubling the frequency doubles the photon's energy. A gamma-ray photon carries far more energy than a radio photon. But be careful not to confuse a single photon's energy with the total power of a beam: a dim blue laser can deliver less total energy per second than a bright red one, even though each blue photon is individually more energetic, because power also depends on how many photons arrive. This tool reports the per-photon energy, E = h·f.

Why is the spectrum band the same even when I change the medium?

Because the band is classified from the vacuum wavelength, not the in-medium one. When light enters water or glass its wavelength shortens, but its frequency — and therefore its photon energy and its identity as, say, green light — does not change. Classifying by the shortened in-medium wavelength would wrongly shift green light toward blue. So the tool always converts back to the vacuum wavelength (c/f) before deciding the band, which matches how physicists name electromagnetic radiation.

Convert a laser's wavelength to its photon energy

A lab spec sheet lists a diode laser as 532 nm but your detector datasheet is calibrated in eV. Type 532 in nm, read back 2.33 eV and 5.64 × 10¹⁴ Hz, and you have the photon energy without hunting for h·c/λ on a napkin. The visible-band tag confirms 532 nm is green, which matches the laser's colour — a quick sanity check that you entered the right wavelength.

Find the wavelength of a Wi-Fi or radio signal

Your router runs at 2.4 GHz and you want the wavelength to reason about antenna size. Switch to frequency input, type 2.4, pick GHz, and read 12.5 cm. The tool tags it microwave, so you know a quarter-wave antenna is around 3 cm. Same workflow for an FM station at 98 MHz (about 3.06 m, radio band) or a 60 GHz 802.11ad link (5 mm).

Check an ionisation-energy problem in chemistry

A homework question gives a photon energy of 13.6 eV and asks for the wavelength that would ionise hydrogen. Switch to photon-energy input, type 13.6, choose eV, and read about 91.2 nm — squarely in the ultraviolet, the Lyman-limit you expected. Because frequency is the invariant, the energy-to-wavelength conversion uses the vacuum value, so the answer matches the textbook.

Teach the inverse relationship between λ and f

In class you want to show that halving the wavelength doubles the frequency. Put 600 nm in and note 5.00 × 10¹⁴ Hz; change it to 300 nm and watch the frequency jump to 9.99 × 10¹⁴ Hz. Sharing the URL with each value pre-filled lets students reproduce the exact two states you demonstrated, turning a hand-wave into a reproducible experiment.

Compare in-medium wavelengths across glass and water

A 589 nm sodium line travels through air, water, and glass. Enter 589 nm with vacuum c, then switch to refractive index and type 1.33, then 1.50, watching the wavelength shrink to about 443 nm and 393 nm while the frequency and the "yellow / visible" classification stay put. It makes concrete why we say the colour does not change when light enters glass — only its speed and wavelength do.

Wavelength ↔ Frequency ↔ Photon Energy Calculator

Convert between wavelength λ, frequency f, and photon energy E · c = λf · E = hf · spectrum band + visible colour · browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Value

Wave speed

Wave speed in use: 2.9979e+8 m/s

Results

Wavelength λ: 500 nm
Frequency f: 599.585 THz
Photon energy E: 2.47968 eV
Spectrum band: Visible light · cyan

What this tool does

Type any one of wavelength λ, frequency f, or photon energy E and this calculator solves the other two from the two relations every physics course leans on: c = λ·f and E = h·f. The speed of light and Planck's constant are the CODATA exact values (c = 299 792 458 m/s, h = 6.626 070 15 × 10⁻³⁴ J·s), so a 500 nm green photon comes back as 5.996 × 10¹⁴ Hz and 2.48 eV — the numbers your textbook prints. Wavelength accepts nm, µm, mm, cm, m, and ångström; frequency runs Hz through THz; energy switches between joules and electronvolts in one click. The wave speed is editable: keep vacuum c, type a custom speed for sound or another medium, or enter a refractive index n so the in-medium speed becomes c/n (water n ≈ 1.33, glass n ≈ 1.5). Photon energy always derives from the frequency — which stays invariant when light enters a medium — so E never drifts with the shortened in-medium wavelength. Every result is classified into an electromagnetic band (radio, microwave, infrared, visible, ultraviolet, X-ray, gamma) from its vacuum wavelength, and visible light gets an approximate colour name. Inputs sync to a shareable URL, and one click copies all four results.

Tool details

Input: Text + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 11 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Wavelength Frequency Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Convert a laser's wavelength to its photon energy
A lab spec sheet lists a diode laser as 532 nm but your detector datasheet is calibrated in eV. Type 532 in nm, read back 2.33 eV and 5.64 × 10¹⁴ Hz, and you have the photon energy without hunting for h·c/λ on a napkin. The visible-band tag confirms 532 nm is green, which matches the laser's colour — a quick sanity check that you entered the right wavelength.
Find the wavelength of a Wi-Fi or radio signal
Your router runs at 2.4 GHz and you want the wavelength to reason about antenna size. Switch to frequency input, type 2.4, pick GHz, and read 12.5 cm. The tool tags it microwave, so you know a quarter-wave antenna is around 3 cm. Same workflow for an FM station at 98 MHz (about 3.06 m, radio band) or a 60 GHz 802.11ad link (5 mm).
Check an ionisation-energy problem in chemistry
A homework question gives a photon energy of 13.6 eV and asks for the wavelength that would ionise hydrogen. Switch to photon-energy input, type 13.6, choose eV, and read about 91.2 nm — squarely in the ultraviolet, the Lyman-limit you expected. Because frequency is the invariant, the energy-to-wavelength conversion uses the vacuum value, so the answer matches the textbook.
Teach the inverse relationship between λ and f
In class you want to show that halving the wavelength doubles the frequency. Put 600 nm in and note 5.00 × 10¹⁴ Hz; change it to 300 nm and watch the frequency jump to 9.99 × 10¹⁴ Hz. Sharing the URL with each value pre-filled lets students reproduce the exact two states you demonstrated, turning a hand-wave into a reproducible experiment.
Compare in-medium wavelengths across glass and water
A 589 nm sodium line travels through air, water, and glass. Enter 589 nm with vacuum c, then switch to refractive index and type 1.33, then 1.50, watching the wavelength shrink to about 443 nm and 393 nm while the frequency and the "yellow / visible" classification stay put. It makes concrete why we say the colour does not change when light enters glass — only its speed and wavelength do.

Common pitfalls

Forgetting frequency stays constant in a medium. When light enters glass or water its wavelength shrinks but its frequency — and thus its photon energy and colour — do not. This tool ties energy to frequency and classifies the band from the vacuum wavelength so you never mislabel an in-medium value.
Mixing up per-photon energy with beam power. E = h·f is the energy of one photon; a bright red beam can carry more total power than a dim blue one even though each blue photon is more energetic. Read this tool's energy as per-photon, not total.
Entering frequency in Hz when you meant THz (or vice versa). Visible light is hundreds of THz, not Hz — a typo of the unit picker shifts the answer by twelve orders of magnitude. Glance at the spectrum band — if a "visible" input lands in radio, you picked the wrong frequency unit.

Privacy

Every conversion — c = λ·f, E = h·f, the unit changes, the refractive-index speed, and the spectrum classification — is plain JavaScript that runs in your browser tab. No wavelength, frequency, or energy you enter ever leaves the page, nothing is logged, and there is no external API call. The one thing to note: the shareable URL encodes your current input and unit choices in the query string, so a "share link" lets the destination server's access log see those values. For coursework that is harmless; copy the result text instead if a number is for some reason sensitive.

FAQ

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Wavelength ↔ Frequency ↔ Photon Energy Calculator

Results

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Wavelength Frequency Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Convert a laser's wavelength to its photon energy

Find the wavelength of a Wi-Fi or radio signal

Check an ionisation-energy problem in chemistry

Teach the inverse relationship between λ and f

Compare in-medium wavelengths across glass and water

Common pitfalls

Privacy

FAQ

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