The surface gravity for a planet can be calculated from its mass and radius.

Planetary Data
Planet	Mass ( kg )	Radius ( m )
Moon	7.35e22	1,738,000
Mars	6.42e23	3,397,000
Earth	5.97e24	6,378,000

Surface gravity = 6.67e-11 ( N * m^2 / kg^ 2 ) * mass / radius^2
 

Gravity is defined as the gravitational acceleration at the surface of a body towards the center of that body. Increasing gravity makes it more difficult to reach an orbit because the craft has to use an increasing portion of its mass for the rocket engine, an increasingly dense atmosphere will be retained which increases the aerodynamic resistance the rocket must face and the orbital velocity will increase. Gravity is used to calculate angle at each moment, column height and ground orbital velocity.

Column height = 8314 ( J * K / kmol ) * temperature / molecular weight / gravity

Ground orbital = sqrt( radius * gravity )
 

This is used in atmospheric spacecraft, multi stage spacecraft, and spacecraft cost.
 

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