Here's the full math
1g (gravity) = 9.81 m/s2 (acceleration)
Force = mass * acceleration
if your ship weighs 1000kg that means its gravitational Force (F) on a planet with 1g = .
F=m*a
F=1000 * 9.81
F= 9810 Newton
If you have 9810 of force exactly opposed (straight into the sky), you would neither fall or climb. you need your acceleration (a) to be more than that 9.81 which means either "F" has to go up, or "m" has to come down.
On planets with a gravity less than 1g, just use this formula : Force (N) = mass (kg) * gravity (g) * 9.81