Flux Density, B, of a Cylindrical Magent

Hi, I'm trying to calculate the flux density of a magnet, I can get all but one of the values needed to calculate it. Does anyone know how/where to get the z(distance from a pole face on the symmetrical axis) value?

 

Thanks for responding, It's for school but it feels more like a hobby, I was thinking of just assuming a value for z. I'm studying mechanical engineering so electrical isn't my strong point. But I believe it might be a set value, maybe a distance from the pole face to the height of the flux field? but then I don't know the height of the flux field anyway

My reason for thinking its a set value is because the flux density of the magnet shouldnt change with respect to z not so?

 

Oh okay thanks!!

but what if the distance I wanted to calculate B for is horizontally across from the magnet instead of vertically away from it? A different formula?