This is how to calculate the escape velocity
v = sqrt(2*G*M/R
and the gravitation
g = G*M/R^2
v = escape velocity [m/s],
g = gravitation [m/s^2],
M = mass of the planet [kg],
R = distance from its center or radius [m] and
G = gravitational constant = 6.673x10^-11
Now you can test different planets and moons and even the sun itself.
If you calculate the density of Saturn by dividing its mass with its volume you'll find that its density is very low - even less than water, and therefore its radius is larger than it should be if it just was a rocky planet like the Earth.