What is the gravitational constant G to four significant figures?

The gravitational constant G to four significant figures is 6.674×10⁻¹¹ N·m²/kg². It is the proportionality constant in Newton’s law of universal gravitation, F = Gm₁m₂/r², linking the masses of two objects and the distance between them to their mutual gravitational force.

G is often called “big G” to distinguish it from lowercase g, the local acceleration caused by gravity near Earth’s surface. Unlike g, which varies slightly with latitude and altitude, G is treated as a universal constant. Its SI units can also be written as m³·kg⁻¹·s⁻².

The value is unusually difficult to measure because gravity is extremely weak in laboratory experiments. Henry Cavendish’s 1798 torsion-balance experiment made the first successful direct measurement of gravitational attraction between laboratory masses, although his stated goal was to “weigh the Earth.”

Modern measurements give approximately 6.67430×10⁻¹¹ m³·kg⁻¹·s⁻², which rounds to the stored answer at four significant figures. A common mix-up is choosing 9.8 m/s², which is Earth’s approximate g, not G.