Planck Equation Calculator

How it works

1. 1Select whether to find energy from a known frequency, or frequency from a known energy.
2. 2Enter the frequency in hertz (Hz) or the energy in electronvolts (eV).
3. 3The calculator applies the Planck–Einstein relation E = h·f and shows results in joules/eV and Hz/THz.

Use cases

• Find the energy of a visible-light photon (≈ 400–700 THz) for optics coursework.
• Convert a photon energy in eV (e.g. a semiconductor band gap) into the light frequency.
• Verify quantum-mechanics homework on the Planck relation between frequency and energy.

Frequently asked questions

What is the Planck–Einstein relation?

E = h·f states that the energy E of a single photon equals the Planck constant h (6.626×10⁻³⁴ J·s) times the photon’s frequency f in hertz. Planck proposed it in 1900 and Einstein extended it in 1905 to explain the photoelectric effect.

What is the Planck constant and its units?

The Planck constant h = 6.626×10⁻³⁴ J·s (joule-seconds) sets the scale of quantum effects and is exact under the 2019 SI redefinition. The reduced form ħ = h ÷ 2π ≈ 1.055×10⁻³⁴ J·s appears in atomic physics, but the Planck equation uses the unreduced h.

What is a quantum of energy, with a worked example?

A quantum of energy is the smallest packet of electromagnetic energy at a frequency — one photon. Green light at f = 5×10¹⁴ Hz: E = 6.626×10⁻³⁴ × 5×10¹⁴ ≈ 3.31×10⁻¹⁹ J ≈ 2.07 eV.