Free · Waves and optics

Spectral Redshift from Wavelength or Frequency

Calculate dimensionless redshift or blueshift from positive emitted and observed vacuum wavelengths or frequencies.

Calculator inputs

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Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
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An emitted wavelength of 500 nm observed at 750 nm has z = 0.5. If observed at 400 nm instead, z = −0.2, a blueshift.

z = observed wavelength ÷ emitted wavelength − 1 = emitted frequency ÷ observed frequency − 1

Enter these known values and leave the other values blank.

Frequencies and wavelengths are positive. Their product uses the exact vacuum light speed 299,792,458 m/s.
The shift must exceed −1. A value of zero means equal emitted and observed wavelengths.
This calculation identifies a spectral shift; it does not infer recession velocity, distance, cause or cosmological parameters.

Yes. Values between −1 and zero represent an observed wavelength shorter than the emitted wavelength.

No. A velocity interpretation requires an additional physical model and assumptions.

Bookify requires spectral redshift to exceed minus one, consistent with positive frequencies and wavelengths.