Case 1
- Recession velocity
- 7000km/s
- Hubble constant H₀
- 70km/s/Mpc
100.000000Mpc
Open with these valuesHubble's Law Calculator
100.000000Mpc
Result: 100.000000 MpcDivide the recession velocity by the Hubble constant and you get the distance in megaparsecs. The catch is the constant itself: the early universe says about 67.4, nearby supernovae say about 73, and that unresolved 8 percent gap shifts every distance below by the same 8 percent.
Worked examples
Case 2
- Recession velocity
- 10000km/s
- Hubble constant H₀
- 67.4km/s/Mpc
148.367953Mpc
Open with these valuesCase 3
- Recession velocity
- 10000km/s
- Hubble constant H₀
- 73km/s/Mpc
136.986301Mpc
Open with these valuesHow it's calculated
d = v ÷ H₀
- StepEnter the galaxy's recession velocity in km/s.
- StepChoose a Hubble constant — 67.4 and 73 are the two contested values.
- StepDivide velocity by constant to get the distance in megaparsecs.
- ResultMultiply by 3.26156 for millions of light-years.
Reference table
| Velocity, H₀ | Where the H₀ comes from | Distance (Mpc) |
|---|---|---|
| 7000, 70 | round convention, neither camp | 100 |
| 10000, 67.4 | Planck, the early universe | 148.367953 |
| 10000, 73 | SH0ES, nearby supernovae | 136.986301 |
| 21000, 70 | round convention | 300 |
| 14000, 70 | round convention | 200 |
| 5000, 73 | SH0ES, nearby supernovae | 68.493151 |
Questions
How do I calculate distance with Hubble's law?
Divide the galaxy's recession velocity by the Hubble constant: d = v / H₀. With the velocity in km/s and H₀ in km/s per megaparsec, the distance comes out in megaparsecs. A galaxy receding at 7000 km/s with H₀ = 70 sits at 100 Mpc, about 326 million light-years.
What value should I use for the Hubble constant?
There is no settled answer, which is why this calculator asks rather than decides. Measurements of the early universe from the cosmic microwave background give about 67.4 km/s/Mpc, while Cepheids and supernovae in the nearby universe give about 73. The two disagree by more than either error bar allows.
What is the Hubble tension?
It is the name for that unresolved roughly 8 percent gap between the early-universe and late-universe values of H₀. Because distance is velocity divided by H₀, the same galaxy sits at 137 Mpc under 73 and at 148 Mpc under 67.4. Nobody yet knows whether the cause is a measurement error or new physics.
How many light-years are in a megaparsec?
One megaparsec is about 3.26156 million light-years, since one parsec is 3.26156 light-years. Multiply the result above by 3.26156 to read it that way.
When does Hubble's law stop being accurate?
It is a good approximation for galaxies far enough away that cosmic expansion dominates their motion. Nearby galaxies also drift under local gravity, which adds scatter, and for very distant objects the simple linear relation gives way to a full cosmological model.
Sources and last check
Information, not professional advice.