# Gravitational constant

The **gravitational constant** (also known as the **universal gravitational constant**, the **Newtonian constant of gravitation**, or the **Cavendish gravitational constant**),[lower-alpha 1] denoted by the letter *G*, is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general theory of relativity.

Values of G | Units |
---|---|

6.67430(15)×10^{−11} m^{3}⋅kg^{−1}⋅s^{−2}[1] |
m^{3}⋅kg^{–1}⋅s^{–2} |

6.67430(15)×10^{−8} |
dyne cm^{2}⋅g^{–2} |

4.30091(25)×10^{−3} |
pc⋅M_{⊙}^{–1}⋅(km/s)^{2} |

In Newton's law, it is the proportionality constant connecting the gravitational force between two bodies with the product of their masses and the inverse square of their distance. In the Einstein field equations, it quantifies the relation between the geometry of spacetime and the energy–momentum tensor (also referred to as the stress–energy tensor).

The measured value of the constant is known with some certainty to four significant digits. In SI units, its value is approximately 6.674×10^{−11} m^{3}⋅kg^{−1}⋅s^{−2}.[1]

The modern notation of Newton's law involving *G* was introduced in the 1890s by C. V. Boys. The first implicit measurement with an accuracy within about 1% is attributed to Henry Cavendish in a 1798 experiment.[lower-alpha 2]