Well...are you talking locally or universally?
If locally, we usually use the formula:
W = m*g
W is the gravitational force acting on the object of interest
m is its mass
g is the local gravitational field strength, a property of the region of space where it resides (notice that I am avoiding calling this "acceleration of gravity").
If universally, we can use the formula:
Fgrav = G*M*m/r^2
Where:
G is Cavendish's measured proportionality constant, assumed to be universal
M is the mass of one of the bodies of interest
m is the mass of the other of the bodies of interest
r is the separation distance