What Is a Hubble's Law Distance Calculator?
Hubble's Law states that a galaxy's recession velocity is proportional to its distance: v = H0 × d. This calculator rearranges that relationship to estimate a galaxy's distance from its redshift and a chosen value for the Hubble constant, H0 — the same basic method used to derive rough distances to galaxies too far away for direct measurement.
Redshift happens because the universe's expansion stretches the wavelength of light in transit; the more a galaxy's spectral lines have shifted toward red, the faster it is receding and, by Hubble's Law, the farther away it is.
How to Read Your Results
Estimated Distance
The primary result, in megaparsecs (Mpc) — the standard astronomical distance unit for cosmological scales (1 Mpc ≈ 3.26 million light-years).
Recession Velocity
The speed at which the galaxy is moving away from us, estimated from redshift using v = cz.
Distance in Light-Years
The same distance converted to millions of light-years, often a more intuitive unit for a general audience.
Hubble Constant Used
Confirms which value of H0 was applied, since published estimates of H0 range from about 67 to 73 km/s/Mpc depending on the measurement technique — a real, unresolved discrepancy in cosmology known as the "Hubble tension."
Real-World Example
A galaxy is measured with a redshift of z = 0.02. Using H0 = 70 km/s/Mpc:
| Quantity | Value |
|---|---|
| Redshift (z) | 0.02 |
| Recession velocity | ≈ 5,996 km/s |
| Estimated distance | ≈ 85.7 Mpc (≈ 280 million ly) |
Tips for Using This Calculator
- This v = cz approximation is only reliable for small redshifts (roughly z < 0.1) — at higher redshifts, relativistic effects require a full cosmological model.
- Try a range of H0 values (67–73) to see how sensitive the distance estimate is to the ongoing Hubble tension debate.
- Local galaxies also have their own "peculiar velocity" from gravitational interactions, which adds noise to redshift-based distance estimates at close range.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team