Hubble's Law Calculator
Enter a galaxy's recession velocity and the Hubble constant to get its distance with Hubble's law — in megaparsecs and millions of light-years.
Distance two ways at once
Enter the recession velocity and the Hubble constant and the calculator returns the distance in megaparsecs and in millions of light-years together.
Mind the Hubble constant
The result depends on H₀. Modern estimates cluster near 70 km/s/Mpc, but the exact value is still debated — the Hubble tension.
What is Hubble's law?
Velocity tells you distance
This Hubble's law calculator turns a galaxy's recession velocity into its distance. Hubble's law says that the speed at which a galaxy moves away from us is proportional to how far away it is: v = H₀ × d, where H₀ is the Hubble constant, the present-day rate of cosmic expansion. Rearranged to d = v / H₀, the relation becomes a distance estimator — feed in a velocity (often measured from a galaxy's redshift) and the expansion rate, and out comes the distance. It is one of the foundations of modern cosmology and the simplest way to gauge how far away the most distant galaxies lie.
Enter a recession velocity in km/s and a Hubble constant in km/s/Mpc to get the distance in megaparsecs and millions of light-years instantly.
The distance is the recession velocity divided by the Hubble constant, and the same distance converts to light-years using a fixed factor.
d = v / H₀With the velocity in km/s and H₀ in km/s per megaparsec, the units of velocity cancel and the distance comes out in megaparsecs. To express it in millions of light-years, the calculator multiplies by 3.26156, since one megaparsec equals about 3.26156 million light-years.
Suppose a galaxy is receding at 7000 km/s and you adopt a Hubble constant of 70 km/s/Mpc.
Divide velocity by H₀
7000 / 70 = 100 — the distance in megaparsecs.
State the distance in Mpc
The galaxy lies about 100 Mpc away — the standard astronomical distance unit.
Convert to light-years
100 × 3.26156 ≈ 326.156 — about 326 million light-years away.
The distance in megaparsecs (100 Mpc above) is the figure astronomers use directly, while the light-years version (about 326 million) is easier to picture: light leaving that galaxy set out roughly 326 million years ago. Because distance is velocity divided by H₀, the result is only as certain as the Hubble constant you choose — a smaller H₀ stretches every distance, a larger one shrinks it. That is why two careful astronomers can report different distances for the same galaxy depending on whether they favour a value near 67 or near 73 km/s/Mpc. Treat the output as a well-grounded estimate rather than an exact figure, and keep both numbers in view: the megaparsec value for calculation and the light-year value for intuition.
Hubble's law is simple and powerful, but a couple of caveats shape how far you can trust the answer.
The Hubble constant is still debated
The value of H₀ is not settled: early-universe measurements favour about 67 km/s/Mpc while local measurements favour about 73, a roughly 9% gap known as the Hubble tension that propagates straight into your distance. The linear law also works best for distant galaxies — nearby ones have their own peculiar motions, and at very large redshifts a full cosmological model is needed rather than this simple proportion.