Observed values of the Hubble constant H ([1]).

The proportionality between recession velocity and distance in the Hubble Law is called the Hubble constant, or more appropriately the Hubble parameter.

The Particle Data Group documents quote a "best modern value" of the Hubble constant as . This value comes from the use of type Ia supernovae (which give relative distances to about 5%) along with data from Cepheid variables gathered by the Hubble Space Telescope. The value from the WMAP survey is 71 km/s per Megaparsec.

The Hubble parameter has the dimensions of inverse time, so a Hubble time t_H may be obtained by inverting the present value of the Hubble parameter.

Date published	H (km/s)/Mpc	Observer	Citation	Remarks / methodology
2018-02-22	73.45±1.66	Hubble Space Telescope	^[15]^[16]	Parallax measurements of galactic cepheids; the value suggests a discrepancy with CMB measurements at the 3.7σ level. The uncertainty is expected to be reduced to below 1% with the final release of the Gaia catalog.
2017-10-16	70.0+12.0 −8.0	The LIGO Scientific Collaboration and The Virgo Collaboration	^[17]	Measurements are independent of a cosmic ‘distance ladder'; the gravitational-wave analysis directly estimates the luminosity distance out to cosmological scales.
2016-11-22	71.9+2.4 −3.0	Hubble Space Telescope	^[18]	Uses time delays between multiple images of distant variable sources produced by strong gravitational lensing.
2016-07-13	67.6+0.7 −0.6	SDSS-III Baryon Oscillation Spectroscopic Survey	^[19]	Baryon acoustic oscillations
2016-05-17	73.24±1.74	Hubble Space Telescope	^[20]	Type Ia supernova, the uncertainty is expected to go down by a factor of more than two with upcoming Gaia measurements and other improvements.
2015-02	67.74±0.46	Planck Mission	^[21]^[22]	Results from an analysis of Planck's full mission were made public on 1 December 2014 at a conference in Ferrara, Italy. A full set of papers detailing the mission results were released in February 2015.
2013-10-01	74.4±3.0	Cosmicflows-2	^[23]	Comparing redshift to other distance methods, including Tully-Fisher, Cepheid variables, and Type I supernovae
2013-03-21	67.80±0.77	Planck Mission	^[24]^[25]^[26]^[27]^[28]	The ESA Planck Surveyor was launched in May 2009. Over a four-year period, it performed a significantly more detailed investigation of cosmic microwave radiation than earlier investigations using HEMT radiometers and bolometer technology to measure the CMB at a smaller scale than WMAP. On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's data including a new CMB all-sky map and their determination of the Hubble constant.
2012-12-20	69.32±0.80	WMAP (9-years)	^[29]
2010	70.4+1.3 −1.4	WMAP (7-years), combined with other measurements.	^[30]	These values arise from fitting a combination of WMAP and other cosmological data to the simplest version of the ΛCDM model. If the data are fit with more general versions, H₀ tends to be smaller and more uncertain: typically around 67±4 (km/s)/Mpc although some models allow values near 63 (km/s)/Mpc.^[31]
2010	71.0±2.5	WMAP only (7-years).	^[30]
2009-02	70.1±1.3	WMAP (5-years). combined with other measurements.	^[32]
2009-02	71.9+2.6 −2.7	WMAP only (5-years)	^[32]
2007	70.4+1.5 −1.6	WMAP (3-years)	^[33]
2006-08	77.6+14.9 −12.5	Chandra X-ray Observatory	^[34]
2001-05	72±8	Hubble Space Telescope	^[35]	This project established the most precise optical determination, consistent with a measurement of H₀ based upon Sunyaev-Zel'dovich effect observations of many galaxy clusters having a similar accuracy.
prior to 1996	50–90 (est.)		^[36]
early 1970s	~55 (est.)	Allan Sandage and Gustav Tammann	^[37]
1958	75 (est.)	Allan Sandage	^[38]	This was the first good estimate of H₀, but it would be decades before a consensus was achieved.

Estimated values of the Hubble constant, most recent at left. (Horizontal axis not temporally proportional)