The thckness of the structural concrete floor normally depends on the type of floor and the spans involved.
The thickness of the structural floor is usually 150 - 225mm.
But in this case, I am assuming you are referring to the cement:sand floor screed which is laid on top of the concrete structural floor.
The floor screed should be reinforced with either chicken wire or have fibres as reinforcement added to the mix.
The generally minimum recommended thickness is 50mm.
The NHBC standards Part 8.3 - S2 state that
"THICKNESS: Screeds should be laid to the specified thickness"
"There should be at least 25mm thickness of screed above the highest point of any service pipe or insulation placed around the pipe."
"SURFACE PREPARATION: All surfaces should be clean and dust free. In particular, any traces of gypsum should have been removed.
Concrete surfaces should be wetted and brushed before screeding."
Screeds should not be as thin as 10mm anywhere, but especially at doorways, where they are almost certain to break up and fail.
You may also be talking about the levelling compound (aka Latex) sometimes used to smooth out rough surfaces.
This is applied as a liquid and can be any thickness often quite thin. It is very smooth and black in colour.