Dark Energy Density Calculator
The dark energy density calculator computes the critical density of the universe, the dark energy density, the cosmological constant Lambda, and the dark matter density from the Hubble constant and density parameters. Dark energy is the dominant component of the universe, comprising about 68.5% of its total energy content according to Planck 2018 CMB measurements. It is responsible for the observed acceleration of cosmic expansion, first discovered by the SCP and High-Z Supernova teams in 1998 and recognised with the 2011 Nobel Prize in Physics. This tool uses Planck 2018 baseline cosmological parameters by default, which can be adjusted to explore other cosmological models.
Dark energy formulas
Critical density: rho_c = 3*H0^2 / (8*pi*G)
Dark energy density: rho_Lambda = Omega_Lambda * rho_c
Matter density: rho_m = Omega_m * rho_c
Cosmological constant: Lambda = 8*pi*G*rho_Lambda / c^2
G = 6.674e-11 N*m^2/kg^2; c = 2.998e8 m/s
Planck 2018 baseline cosmological parameters
- H0 = 67.4 +/- 0.5 km/s/Mpc
- Omega_Lambda = 0.6847 +/- 0.0073
- Omega_m = 0.3153 +/- 0.0073
- Omega_b (baryons) = 0.0493 +/- 0.0022
- rho_c = 8.62e-27 kg/m^3 for H0 = 67.4 km/s/Mpc
Dark energy: frequently asked questions
What is dark energy?
Dark energy is the name given to the unknown component of the universe responsible for its accelerating expansion. It makes up approximately 68.5% of the total energy density of the universe (Planck 2018). The simplest model is a cosmological constant (Lambda) with constant energy density rho_Lambda = Lambda*c^2/(8*pi*G). Dark energy has negative pressure (w = p/rho = -1 for cosmological constant), causing the expansion to accelerate.
What is the cosmological constant?
The cosmological constant Lambda was originally introduced by Einstein in 1917 to allow for a static universe. After Hubble's 1929 discovery of cosmic expansion, Einstein discarded it. In 1998, supernova surveys discovered that the expansion is accelerating, reviving Lambda as dark energy. The Planck 2018 value: Lambda = 1.10e-52 m^-2 = 1.10e-35 s^-2 / c^2. The corresponding energy density is rho_Lambda = Lambda*c^2/(8*pi*G).
What is the critical density of the universe?
The critical density is the total energy density needed for a flat (Omega = 1) universe: rho_c = 3*H0^2/(8*pi*G). For H0 = 67.4 km/s/Mpc: rho_c = 8.62e-27 kg/m^3, equivalent to about 5 proton masses per cubic meter. The universe is observed to be very close to flat (Omega_total = 1.00 within 0.5%), confirming inflation's prediction.
What are the density parameters of the universe?
Planck 2018 results: Omega_Lambda (dark energy) = 0.6847 +/- 0.0073. Omega_m (total matter) = 0.3153 +/- 0.0073. Omega_b (baryonic matter) = 0.0493 +/- 0.0022. Omega_CDM (cold dark matter) = 0.2660 +/- 0.0022. Omega_total = Omega_Lambda + Omega_m = 1.0000 (flat universe). The total energy density equals the critical density.
What is the cosmological constant problem?
Quantum field theory predicts a vacuum energy density of about 10^113 J/m^3 (Planck density). The observed cosmological constant corresponds to an energy density of about 6e-10 J/m^3. The discrepancy is a factor of about 10^123, the largest unexplained discrepancy in all of physics. This is the cosmological constant problem, one of the deepest unsolved problems in theoretical physics and cosmology.
Official sources
- ESA Planck 2018: Planck 2018 Cosmological Parameters (ESA).
- NASA: NASA LAMBDA Cosmological Parameters.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.