Redshift Calculator
Compute cosmological redshift z and recession velocity from observed and emitted wavelengths.
Input Data
Observed wavelength (nm or any consistent unit).
Rest-frame emitted wavelength (same unit).
Results
0
0
Redshift z = 0; recession v = 0 km/s.
At a glance:Redshift z = (λ_obs − λ_emit)/λ_emit. Recession velocity uses relativistic v = c·((1+z)²−1)/((1+z)²+1), c = 299792.458 km/s.
Formula
z = (λ_obs − λ_emit) / λ_emit.
v = c·((1+z)² − 1) / ((1+z)² + 1).
How to Use
- Enter observed and emitted wavelengths (same unit).
- The tool returns z and recession velocity.
Case Studies
λ_obs=700, λ_emit=656.3 → z≈0.0666, v≈19700 km/s
z = 43.7/656.3 ≈ 0.0666; relativistic v ≈ 19700 km/s.
FAQ
Negative z?
Blueshift, the source is approaching.
Low-speed approx?
For z≪1, v≈c·z.
Related Tools
References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.