Hubble Law Calculator
Calculate galaxy recession velocity from Hubble's Law (v = H₀d). Shows Hubble tension between Planck (67.4) and SH0ES (73.0) values. Includes Hubble time and critical density.
Mpc
km/s/Mpc
Recession Velocity
—
Approx. Redshift (low-z) —
Hubble Time —
Extended More scenarios, charts & detailed breakdown ▾
Mpc
km/s/Mpc
Recession Velocity
—
Approx. Redshift —
Hubble Time —
Professional Full parameters & maximum detail ▾
Mpc
km/s/Mpc
Recession
Recession Velocity —
Redshift (low-z) —
Universe Properties
Hubble Time —
Hubble Distance c/H₀ —
Critical Density ρ_c —
How to Use This Calculator
- Enter the distance to the galaxy in megaparsecs and the Hubble constant (default 70).
- The result shows recession velocity, redshift estimate, and Hubble time.
- Use Solve for Distance tab if you know velocity.
- See Hubble Constant Sources tab to compare Planck vs SH0ES values and understand the tension.
Formula
v = H₀ × d | H₀ in km/s/Mpc, d in Mpc
Hubble time: t_H = 1/H₀ ≈ 978 Gyr × (100/H₀)
Critical density: ρ_c = 3H₀² / (8πG)
Example
Andromeda (M31): d = 0.778 Mpc, H₀ = 70 → v = 70 × 0.778 = 54.5 km/s (actually approaching due to local gravity, illustrating Hubble Law is for cosmological scales).
Frequently Asked Questions
- Hubble's Law states that galaxies recede from us at a velocity proportional to their distance: v = H₀ × d, where H₀ is the Hubble constant (km/s/Mpc) and d is the distance in megaparsecs.
- The Hubble constant H₀ describes the current expansion rate of the universe. Planck CMB data gives ~67.4 km/s/Mpc; the SH0ES project (Type Ia supernovae) gives ~73.0 km/s/Mpc. This "Hubble tension" is an active research area.
- Hubble time = 1/H₀ ≈ 13.9 Gyr for H₀ = 70 km/s/Mpc. It gives an estimate of the age of the universe. The actual age (~13.8 Gyr) is close but differs because expansion has not been constant.
- Hubble distance = c/H₀ ≈ 4286 Mpc = 13.97 Gly for H₀ = 70 km/s/Mpc. It represents the distance at which recession velocity equals the speed of light.
- Critical density ρ_c = 3H₀²/(8πG). For H₀ = 70 km/s/Mpc, ρ_c ≈ 9.2×10⁻²⁷ kg/m³. This is the density needed for a flat (Euclidean) universe.
Related Calculators
Sources & References (5) ▾
- NASA WMAP / Planck Cosmology Results — NASA WMAP
- Hubble Space Telescope Key Project — Freedman et al. 2001, ApJ 553
- SH0ES Collaboration — Riess et al. — Riess et al. 2022, ApJL
- ESA Planck Mission Cosmological Parameters — ESA Planck Collaboration
- OpenStax Astronomy, Ch. 28: The Expanding Universe — OpenStax