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Hubble's Law Calculator.

Estimate recession velocity from the Hubble constant and distance.

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Recession velocity: 700

Recession velocity

700.000000

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Use Cases

Astronomy Education

Helps students and enthusiasts understand the relationship between distance and recession velocity in an expanding universe.

Example: Calculate the velocity of a galaxy at 100 Mpc with H0 = 70 km/s/Mpc.

Research Data Analysis

Quickly estimate velocities for given distances when analyzing galaxy survey data or testing cosmological models.

Example: Estimate velocities for a list of galaxies with known distances.

Frequently Asked Questions

What is Hubble's Law?
Hubble's Law states that the recession velocity of a galaxy is directly proportional to its distance from us. The proportionality constant is the Hubble constant (H0), typically expressed in km/s/Mpc. This calculator uses the formula v = H0 × d to estimate the velocity.
What units should I use for distance?
Distance should be entered in megaparsecs (Mpc). One parsec is about 3.26 light-years, and a megaparsec is one million parsecs. The Hubble constant is in km/s/Mpc, so using Mpc for distance gives velocity in km/s.
What is a typical value for the Hubble constant?
Current estimates range from about 67 to 74 km/s/Mpc, depending on the measurement method. For example, Planck satellite data suggest around 67.4 km/s/Mpc, while some distance ladder methods give about 73 km/s/Mpc. You can use any value you like.

Tips & Common Mistakes

Tips

  • Ensure the Hubble constant is in km/s/Mpc and distance in Mpc to get velocity in km/s.
  • Use consistent units: if you have distance in light-years, convert to Mpc first (1 Mpc ≈ 3.26 million light-years).
  • Remember that Hubble's Law is an approximation valid for large distances where peculiar velocities are small.
  • For accurate cosmological calculations, consider using the exact formula that accounts for relativistic effects, but this simple estimate is fine for most educational purposes.

Common Mistakes to Avoid

  • Forgetting to convert distance to Mpc when using a Hubble constant in km/s/Mpc.
  • Using the Hubble constant in different units (e.g., km/s per light-year) without conversion.
  • Assuming the law applies to nearby galaxies where gravitational interactions dominate over cosmic expansion.

Last updated: August 13, 2026