Hubble's Law Recession Velocity Calculator
Calculate galaxy recession speed using Hubble's Law.
Choose from Planck 2018, standard, or local H₀ values.
Includes Hubble sphere check.
Hubble’s Law states that galaxies recede from us at a speed proportional to their distance. The farther away a galaxy is, the faster it moves away from us.
v = H₀ × d
Where:
- v = recession velocity (km/s)
- H₀ = Hubble constant (km/s per Megaparsec)
- d = distance to the galaxy (Megaparsecs or Gigalightyears)
The Hubble constant controversy: There is an ongoing debate about the precise value of H₀:
- Planck 2018 (CMB method): H₀ = 67.4 km/s/Mpc
- Standard value (widely used): H₀ = 70 km/s/Mpc
- Local measurements (distance ladder): H₀ = 73 km/s/Mpc
This discrepancy, known as the Hubble tension, may point to new physics beyond the standard cosmological model.
The Hubble sphere: At a certain distance, the recession velocity equals the speed of light (c). This distance is called the Hubble radius or Hubble sphere:
d_H = c / H₀
Galaxies beyond this radius recede faster than light — they are outside our Hubble sphere. However, light from some of these galaxies can still reach us due to the geometry of spacetime.
Note on lookback time: For nearby galaxies (d « Hubble radius), lookback time ≈ d/c in light-years. For distant galaxies, a full cosmological calculation is needed. The observable universe has a radius of about 46 billion light-years.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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