Redshift to kilometers per second
Type a value in z to get it in km/s instantly.
That's 4.3× as distant as the Coma cluster, while the nearest quasar is 1.58× further. Light from it arrives about 10% longer in wavelength.
Convert the other way: km/s to z
What it means
How far is that?
Distances use a simple Hubble law at 70 km/s per Mpc, which is only a good guide for small z. Beyond about z = 0.1 the real answer depends on the expansion history.
The math
How to convert z to km/s
Redshift is a stretch: 1 + z = observed ÷ emitted wavelength. Speed follows relativistically, v = c × ((1+z)² − 1) ÷ ((1+z)² + 1), and distance from v ÷ H₀ at 70 km/s per Mpc.
Example: 0.1 z = 28,487.1 km/s.
Every unit
Your redshift in every unit
Tables
z to km/s conversion table
| z | km/s |
|---|---|
| 0.001 z | 299.643 km/s |
| 0.01 z | 2,982.94 km/s |
| 0.05 z | 14,615.3 km/s |
| 0.1 z | 28,487.1 km/s |
| 0.5 z | 115,305 km/s |
| 1 z | 179,875 km/s |
| 2 z | 239,834 km/s |
| 3 z | 264,523 km/s |
| 5 z | 283,587 km/s |
| 7 z | 290,568 km/s |
| 11 z | 295,657 km/s |
km/s to z conversion table
| km/s | z |
|---|---|
| 0.001 km/s | 3.336×10⁻⁹ z |
| 0.01 km/s | 3.336×10⁻⁸ z |
| 0.05 km/s | 1.668×10⁻⁷ z |
| 0.1 km/s | 3.336×10⁻⁷ z |
| 0.5 km/s | 1.668×10⁻⁶ z |
| 1 km/s | 3.336×10⁻⁶ z |
| 2 km/s | 6.671×10⁻⁶ z |
| 3 km/s | 1.001×10⁻⁵ z |
| 5 km/s | 1.668×10⁻⁵ z |
| 7 km/s | 2.335×10⁻⁵ z |
| 11 km/s | 3.669×10⁻⁵ z |
Quick answers
Quick answers
- How many km/s is 1 z?
- 1 z is 179,875 km/s.
- How many km/s is 10 z?
- 10 z is 294,878 km/s.
- How many km/s is 0.1 z?
- 0.1 z is 28,487.1 km/s.
The units
About these units
Redshift (z)
The fractional stretch in wavelength, the number astronomers actually publish.
Kilometers per second (km/s)
The recession speed, taken relativistically so it never passes light.
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