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Photon Energy Calculator

Enter a wavelength, a frequency or an energy and get all three from E = hf = hc/λ, in eV, keV, MeV and joules, with the spectral band named and the colour identified for visible light.

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Open Photon Energy Calculator and you get an answer straight away, with no account to create. You will find it under Physics, with E = mc² Calculator (Mass–Energy) and Kinetic energy calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Photon Energy Calculator?

Enter a wavelength, a frequency or an energy and get all three from E = hf = hc/λ, in eV, keV, MeV and joules, with the spectral band named and the colour identified for visible light.

When would I actually use this?

Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.

What is the most common mistake?

Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.

How is Photon Energy Calculator different from E = mc² Calculator (Mass–Energy)?

They sit next to each other but answer different questions: E = mc² Calculator (Mass–Energy) is the one to open when you need it to convert mass into energy and back with a realistic efficiency — 100 % for antimatter, 0.7 % for fusion, 0.09 % for fission — and read the result in joules, kWh, kcal and tonnes of TNT. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Kinetic energy calculator is the closest one after this: Compute kinetic energy from mass and velocity (½mv²).

What else is worth having open alongside it?

Potential energy calculator and Spring potential energy calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Constants are the CODATA values and the formulas are the textbook ones. Most assume an idealised case — no air resistance, no friction, a point mass — and the tool says so where the simplification matters.

Further reading

All guides →
ExplainerWhat Is Kinetic Energy? The KE = ½mv² Formula ExplainedKinetic energy is the energy of motion, given by KE = ½mv². Learn what the formula means, why speed matters most, and see worked examples in joules.ExplainerHooke's Law Explained: F = kx, Real Spring Constants, and Where It Stops HoldingHooke's law says force is proportional to stretch — but only below the elastic limit. Here is F = kx with worked numbers, what a 200 N/m spring actually feels like, and how springs combine.ExplainerProjectile Motion Explained: Range, Height, Flight Time — and Why 45° Is Not Always BestThree formulas cover the whole of projectile motion on level ground. The catch is level ground: the moment launch and landing heights differ, the 45° result stops being true.ComparisonHeat Pump or Gas Boiler: the SCOP Your Local Prices DemandBefore any grant, the price of electricity divided by the price of gas sets a seasonal efficiency the heat pump must beat just to break even on running cost. In late 2025 that number was 1.53 in Portugal and 2.79 in Germany — and on old radiators a German heat pump can cost more to run than the boiler it replaced.ComparisonInsulate or Replace the Heating: Which Repays First, and Why the Answer InvertsPut both on one axis — euros paid per kilowatt-hour a year of permanent saving — and the comparison becomes decidable. The same loft job costs 0.83 euros per kilowatt-hour a year in a 1965 house and 5.00 in a 2005 one, a factor of six. That, and not the age of the building by itself, is what inverts the verdict.How-toHow to Estimate the Running Costs of a HomeAdd up energy, water, heating, and maintenance with simple rules of thumb so you know what a home really costs to run each month.