Standard gravity

Standard gravity, usually denoted by g0 or gn, is the nominal acceleration due to gravity at the Earth's surface at sea level. By definition it is equal to exactly 9.80665 m/s2 (approx. 32.174 ft/s2). This value was established by the 3rd CGPM (1901, CR 70).

The symbol g is sometimes also used for standard gravity, but g strictly means the local acceleration due to gravity, which varies depending on one's position on Earth. The symbol g should not be confused with G, the gravitational constant, or g, the abbreviation for gram (which is not italicized). The g (sometimes written "gee") is also used as a unit of acceleration, with the value defined as above; see g-force.

The value of g0 defined above is an arbitrary midrange value on Earth, approximately equal to the acceleration of a body in free fall (in the absence of air resistance) at sea level at a geodetic latitude of about 45.5°. It is larger in magnitude than the average sea level acceleration on Earth, which is about 9.797 645 m/s2. Although the actual strength of gravity on Earth varies according to location (see Earth's gravity), for weights and measures and many calculation purposes the standard gravity figure is used.

The SI unit of acceleration due to gravity (or, indeed, any acceleration), namely metre per square second, can also be written as newton per kilogram. The value stays the same: gn = 9.80665 N/kg. This alternative representation for the same unit may be more intuitive when considering problems involving pressure due to gravity, or weight. For example, at sea level the gravitational force between the Earth and a mass of 1 kilogram is 9.80665 newtons.