The only way to know for sure is to run the landing gear out until you hear the motor start to work. But be ready to let go of the button the moment you hear that.
I did it for the up limit, then extended the legs a half inch and painted a line on the legs. That way I know when I am about to "hit bottom", and never have to worry about causing the stress of jamming up the gears again.
But that got me to wondering, is there a stop when one is extending the legs? Maybe they run till the legs fall off? That wouldn't be good!
But I seriously doubt that many people have ever had the need to run them out that far. I would be afraid to park on a site that unlevel.