Hubble's Law Distance Calculator
Calculate galactic recession velocity and distance using Hubble's law.
Enter distance in megaparsecs or redshift to explore the expansion of the universe.
Edwin Hubble announced in 1929 that distant galaxies are receding from us, and that their recession speed is proportional to their distance. This was the first direct evidence that the universe is expanding.
The law
v = H0 x d
Where v is the recession velocity in km/s, d is the distance in megaparsecs (Mpc), and H0 is the Hubble constant in km/s/Mpc.
One megaparsec = 3.086 x 10^22 m = 3.2616 million light-years.
The Hubble constant tension
The value of H0 is currently a major unsolved problem in cosmology — the “Hubble tension.” Measurements from the Cosmic Microwave Background (Planck satellite) give H0 ≈ 67.4 km/s/Mpc. Measurements from the distance ladder (Cepheid variable stars, supernovae) give H0 ≈ 73 km/s/Mpc. The discrepancy is statistically significant and may point to new physics. The default here uses 70 km/s/Mpc as a round number between the two camps.
Redshift
For recession velocities well below c, the redshift is approximately:
z ≈ v / c
where c = 299,792 km/s. The CMB has z ≈ 1100 — it was emitted when the universe was 1,101 times smaller than today.
Lookback time
For nearby galaxies (d « c/H0 ≈ 4,300 Mpc), the lookback time in years is approximately d x 977.8 billion years per Mpc / (c/H0). This is a rough approximation — accurate only for small redshifts.
The Andromeda galaxy (M31) at 0.78 Mpc is actually approaching us (negative recession velocity) — local gravity overrides Hubble expansion at short distances.