Hubble's Law Calculator

Hubble's Law states that galaxies recede from us at a speed proportional to their distance. The relationship is expressed as v = H₀ × D, where v is the recessional velocity, H₀ is the Hubble constant (~70 km/s/Mpc), and D is the distance in Megaparsecs. It was first observed by Edwin Hubble and Georges Lemaître in the late 1920s and forms the observational foundation for the expanding universe model.

Hubble's Law tells us the universe is expanding — every galaxy (on large scales) is moving away from every other galaxy. The further a galaxy is, the faster it recedes. This implies the universe had a much denser, hotter beginning (the Big Bang), and that the cosmos has been expanding ever since.

The Hubble constant H₀ quantifies the expansion rate of the universe. Its accepted range today is roughly 67–73 km/s/Mpc, but two leading measurement methods give significantly different values — the Cosmic Microwave Background method (Planck) yields ~67.4 km/s/Mpc, while the distance-ladder method (SH0ES) yields ~73.2 km/s/Mpc. This tension, called 'Hubble trouble', remains one of the biggest open problems in cosmology.

Select your desired calculation mode from the dropdown — you can solve for recessional velocity, galaxy distance, the Hubble constant, or redshift. Then enter the known values in the relevant fields and the result is computed instantly. For example, to find how fast a galaxy 100 Mpc away is receding, choose 'Calculate Recessional Velocity', set H₀ = 70 km/s/Mpc and distance = 100 Mpc.

Redshift (z) occurs when light from a distant galaxy is stretched to longer (redder) wavelengths as the galaxy moves away. For low velocities, z ≈ v / c, where c is the speed of light (~299,792 km/s). Astronomers measure redshift spectroscopically and then use Hubble's Law to infer the galaxy's distance. Higher redshift means greater distance and faster recession.

The linear approximation v = H₀ × D is reliable only for relatively nearby galaxies (roughly z < 0.1 or distances below ~400 Mpc). At higher redshifts, special relativistic corrections and the full machinery of general relativistic cosmology are needed, including parameters like matter density (Ωm) and dark energy density (ΩΛ). For precise calculations beyond z ~ 0.3, use a proper cosmological distance calculator.

No. Hubble's Law applies only to objects on cosmological scales — typically galaxy clusters and beyond, separated by tens of Megaparsecs or more. Within our own galaxy, and even within the Local Group, gravitational forces dominate over cosmic expansion, so objects do not follow the Hubble flow. In fact, our nearest large neighbor, the Andromeda Galaxy, is actually moving toward us.

Recessional velocity is the component of a galaxy's motion due to the expansion of space itself, described by Hubble's Law. Peculiar velocity is any additional motion caused by local gravitational interactions (e.g., within a galaxy cluster). Observed velocities combine both; for galaxies far enough away, peculiar velocities are small compared to the Hubble flow and can be ignored for rough distance estimates.