Universe Expansion Calculator — Hubble's Law
Apply Hubble's law (v = H₀ × d) to find how fast any galaxy is receding from us due to cosmic expansion. Enter the galaxy's distance in megaparsecs and the Hubble constant to get the recessional velocity, the Hubble time, and the horizon where v = c.
Mpc
km/s/Mpc
Speed at which the galaxy moves away due to cosmic expansion
- 1
Fraction of speed of light
H₀ × d ÷ c = 70 × 100 ÷ 299,792.458 = 0.023349Values above 1 are allowed — space itself expands faster than light. - 2
Recessional velocity
H₀ × d = 70 × 100 = 7,000
How does this calculator work?
Hubble's law: v = H₀ × d. At H₀ = 70 km/s/Mpc a galaxy 100 Mpc away recedes at 7,000 km/s (2.3% of c). The Hubble radius (~4,280 Mpc) is where v = c. The Hubble time 1/H₀ ≈ 13.97 Gyr gives a rough age estimate. Adjust H₀ between 67–73 to explore the Hubble tension.
Formula
How this is calculated
Hubble's law (1929) states that a galaxy's recessional velocity is proportional to its distance: v = H₀ × d. The Hubble constant H₀ (currently estimated at 67–73 km/s/Mpc, depending on the measurement method) sets the rate — for every extra megaparsec of distance, a galaxy recedes roughly 70 km/s faster. This is not because galaxies are flying through space, but because the space between them is stretching.
At the Hubble radius (d_H = c/H₀ ≈ 4,280 Mpc ≈ 14 billion light-years for H₀ = 70), the recessional velocity equals the speed of light. Galaxies beyond this sphere recede at v > c, which is allowed by general relativity because it is space expanding rather than matter moving through it. They can still be visible because light they emitted in the past reached us when they were closer.
The Hubble time (t_H = 1/H₀) is a rough order-of-magnitude estimate of the age of the universe — approximately 13.97 Gyr for H₀ = 70 km/s/Mpc. The precise ΛCDM age is slightly different because the expansion rate has not been constant (it was slower in the matter-dominated era and is now accelerating). The XY plot shows the linear v–d relationship with the entered galaxy and the v = c horizon both marked.
Frequently asked questions
Yes, and many do. The expansion of space is not limited by the speed of light, which constrains only the motion of objects through space. Galaxies beyond the Hubble radius (~4,280 Mpc for H₀ = 70) recede at v > c. We can still observe some of them because light they emitted in the past reached us when they were at a smaller distance.
The Hubble tension is the discrepancy between two independent measurements of H₀: the early-universe CMB approach (Planck gives ~67.4 km/s/Mpc) and the late-universe distance-ladder approach (~73 km/s/Mpc). The 5σ gap is statistically significant and remains an open problem in cosmology.
A megaparsec (Mpc) is one million parsecs, or about 3.26 million light-years (3.09 × 10¹⁹ km). It is the standard unit for cosmological distances. The Andromeda Galaxy is ~0.78 Mpc away; the observable universe extends ~14,000 Mpc.
Also known as
TG we-Calculate Editorial Team. (2026). Universe Expansion Calculator — Hubble's Law [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/universe-expansion-calculator
TG we-Calculate Editorial Team. "Universe Expansion Calculator — Hubble's Law." TG we-Calculate. 2026. https://we-calculate.com/calculator/universe-expansion-calculator.
TG we-Calculate Editorial Team, "Universe Expansion Calculator — Hubble's Law," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/universe-expansion-calculator
@misc{wecalculate_universe_expansion_calculator, title = {Universe Expansion Calculator — Hubble's Law}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/universe-expansion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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