As a genral rule of thumb..... a lenses DOF will show one third in front and two thirds behind your focus point !
i use this when i use the hyperfocal distance point for maxermizing front to back sharpness.
Its very handy if you have a lens with a depth of feild scale. Some lenses come with a booklet or paper showing them.
if you are after maximizing your depth of feild, you are waisting two thirds of your available DOF by foccusing on infinity.
Your far better off using manual focus for land scape ( whats the rush lol )
You can actualy buy DOF calculation charts. they are in the form of a cardboard wheel, which you turn to match up Focal lengh
aprature, sensor size. Any budding landscape photographer should learn about using hyperfocal distance points.
Just google it ! Im sure there will be hoards of info and will show everything you need to know.
Although it sounds a little complex, its actualy quite easy once the penny drops.