Redshift Calculator: Wavelength, Velocity and Cosmological Distance

Your details

Choose how you want to work: compute z from spectra, convert z to velocity, or derive cosmological distances.
Switch between entering wavelengths (nanometres) or frequencies (terahertz).
Rest wavelength of the spectral line in the lab, e.g. hydrogen-alpha is 656.28 nm.
nm
Wavelength measured in the spectrum of the astronomical object. Longer than emitted means redshift.
nm
Rest frequency of the spectral line, e.g. hydrogen-alpha is about 456.8 THz.
THz
Frequency measured in the spectrum. Lower than emitted means redshift (source receding).
THz
Redshift (z)Moderate redshift
0.20375

Dimensionless redshift parameter from the wavelength or frequency shift

Wavelength shift133.72nm
Recession velocity (relativistic)54,966.48km/s
Recession velocity (v/c)0.18335

Redshift z = 0.20375 detected.

  • The source is receding at about 54966 km/s, which is 18.33% of the speed of light.
  • At z > 0.1, the non-relativistic formula v = zc overestimates speed; the relativistic formula used here is more accurate.
  • The emitted wavelength (656.28 nm) matches the H-alpha spectral line, a common reference for redshift measurement.

Next stepSwitch to Cosmological mode to convert this redshift to a lookback time and comoving distance using a standard Lambda-CDM model.

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