The gravitational constant G
G = 6.67430 × 10⁻¹¹ m³ kg⁻¹ s⁻², with a standard uncertainty of 0.00015 × 10⁻¹¹. That is a relative uncertainty of 2.2 parts in 100,000 — thousands of times worse than most other fundamental constants.
Updated on October 7, 2026
The value
Do not confuse G with g. G is the constant in Newton’s law of gravitation, the same everywhere in the universe. g, the standard acceleration of free fall at Earth’s surface, is 9.80665 m/s² and is a convention about our own planet.
G = 0.000000000067 m³ kg⁻¹ s⁻²
- Value
- 6.6743 × 10⁻¹¹
- Unit
- m³ kg⁻¹ s⁻²
- Standard uncertainty
- 1.5 × 10⁻¹⁵
Source: NIST — CODATA Internationally Recommended Values of the Fundamental Physical Constants (2022)
And the other one: standard gravity g
g is fixed at exactly 9.80665 m/s² by agreement, as a conventional reference value. The real local acceleration varies by about 0.5% between the poles and the equator, and with altitude.
g_n = 9.80665 m s⁻²
- Value
- 9.80665
- Unit
- m s⁻²
- Standard uncertainty
- exact by definition (zero uncertainty)
Source: BIPM — Sistema Internacional de Unidades (SI), 9ª edição
Why G is so hard to pin down
Gravity is extraordinarily weak. To measure G you have to detect the pull between laboratory-sized masses, which is around 10⁻³⁸ times the strength of the electric force between two protons, and you cannot switch gravity off to calibrate. Every experiment fights seismic noise, temperature gradients and the mass of the building itself.
The honest situation is that independent high-quality experiments have disagreed with each other by more than their stated error bars. CODATA deals with that by inflating the uncertainty of the recommended value, which is why G is quoted to six digits while h is quoted exactly.
Source: NIST — CODATA Internationally Recommended Values of the Fundamental Physical Constants (2022)
How to read this page
How to read the numbers here
Every value on "The gravitational constant G" comes from the source named beside its section, never from an estimate of our own with no origin.
Where the data comes from
Each section of "The gravitational constant G" names its official source; the verification date sits at the top of the page.
What the number doesn’t tell you
Atomic weight, molar mass and standard uncertainty are measurement concepts: none of them say anything about a real sample’s purity, physical state or specific isotope.
More about “The gravitational constant G”
G among the constants this site tracks
Of the 9 physical constants this module tracks, only 7 are exact by definition; G sits in the other group, the ones still measured in the lab, which is why "The gravitational constant G" shows an uncertainty next to the value.
The order of magnitude alone says a lot: a value around 10⁻11 needs scientific notation to avoid a row of zeros, which is exactly why physics favours that notation over loose decimals.
Words on this page
Standard uncertainty
The margin attached to a measured value, usually written in parentheses on the last digits. A constant that is "exact by definition" has zero standard uncertainty; a measured one, like the gravitational constant G, always carries some.
Standard definition by BIPM — Bureau International des Poids et Mesures (SI) · Standard uncertainty
Mole
The SI counting unit for atoms, molecules or other entities: one mole is exactly 6.02214076 × 10²³ of them, by the definition fixed in 2019. It is what ties a mass in grams to a number of particles.
Standard definition by BIPM — Bureau International des Poids et Mesures (SI) · Mole
Atomic weight
The average weight of an element’s atoms, weighted by how abundant each isotope is in nature, in atomic mass units. For 14 elements CIAAW publishes a range instead of a single value, because that abundance varies a little from sample to sample.
Standard definition by CIAAW — Commission on Isotopic Abundances and Atomic Weights · Atomic weight
Atomic number
The number of protons in an atom’s nucleus, written Z. It is this number, not the mass, that defines which element an atom is: every atom with 8 protons is oxygen, whether it has 8 or 18 neutrons.
Standard definition by IUPAC · Atomic number
Astronomical unit
The solar system’s reference distance, fixed at exactly 149,597,870,700 metres since 2012, close to the average Earth–Sun distance. It saves writing every planet’s orbit in kilometres with ten digits.
Standard definition by IAU — International Astronomical Union · Astronomical unit