In 1929 Edwin Hubble found that distant galaxies recede faster the farther away they are – the universe is expanding. The Hubble constant is about 67–73 km/s per megaparsec, depending on the method (the “Hubble tension”).
How to use the Hubble’s Law Calculator
- Find
- Hubble constant H₀ (km/s/Mpc)
- Distance d
- Recession velocity v
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose what to find, enter the Hubble constant and the distance or velocity.
Inputs explained
| Field | What to enter |
|---|---|
| Find | Choose one: Recession velocity, Distance |
| Hubble constant H₀ (km/s/Mpc) | A number |
| Distance d | Units: Mpc, Mly, ly |
| Recession velocity v | Units: km/s, c, m/s |
What each result means
- Recession velocity = [H0 SI]×[Distance d]
- Distance = [Recession velocity v]÷[H0 SI]
- Hubble time = 1÷[H0 SI]
Example values
How the main result changes when Hubble constant H₀ changes and everything else stays at the example values above:
| Hubble constant H₀ (km/s/Mpc) | Recession velocity (km/s) |
|---|---|
| 35 | 3,500 |
| 52.5 | 5,250 |
| 70 | 7,000 |
| 87.5 | 8,750 |
| 105 | 10,500 |
| 140 | 14,000 |
Formula
v = H₀·d, z ≈ v/c (for v ≪ c), Hubble time t_H = 1/H₀
Worked example
Inputs — Find: Recession velocity; Hubble constant H₀ (km/s/Mpc): 70; Distance d: 100 Mpc.
Results — Recession velocity = 7,000 km/s; Approximate redshift z = 0.02335; Hubble time = 13.9685 Gyr.
Key terms
- Megaparsec
- One million parsecs, about 3.26 million light-years.
Frequently asked questions
What is the Hubble constant?
The current expansion rate of the universe, about 70 km/s/Mpc.
What is the Hubble tension?
Different methods give ~67 and ~73 km/s/Mpc.
Can galaxies recede faster than light?
Yes, at great distances – space itself expands.
Is the Hubble time the age of the universe?
It is close (about 14 Gyr), but the true age depends on how expansion changed.