1065.630—1980 international gravity formula.

The acceleration of Earth's gravity, a g, varies depending on your location. Calculate a g at your latitude, as follows:
Where:
θ = Degrees north or south latitude.
Example:
θ = 45°
ag = 9.7803267715 · (1
5.2790414 · 10−3 · sin2 (45)
2.32718 · 10−5 ·sin 4 (45)
1.262 · 10−7 ·sin 6 (45)
7 · 10−10 ·sin 8 (45)
ag = 9.8178291229 m/s2