How this calculator works
The ordinary Compton wavelength is Planck constant divided by rest mass times light speed. The reduced wavelength uses hbar instead of h and is smaller by 2pi. Both are characteristic quantum scales; neither is a literal particle diameter. Enter a positive rest mass. A photon has zero rest mass and does not have a finite rest-mass Compton wavelength. The electron default uses the archived CODATA 2018 mass.
Formula
lambdaC = h/(mc); reduced lambdaC = hbar/(mc) = lambdaC/(2pi); rest energy = mc².
Worked example
An electron has ordinary Compton wavelength about 2.426310239 pm and reduced wavelength about 0.386159268 pm. Doubling the mass halves both wavelengths.
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Frequently asked questions
Which wavelength should I use in Compton scattering?
Use the ordinary wavelength h/(mc) in the standard wavelength-shift equation.
Is this the de Broglie wavelength?
No. De Broglie wavelength depends on momentum, whereas Compton wavelength depends on rest mass.
Can the mass be zero?
No finite rest-mass Compton wavelength exists at zero mass.