This height is measured vertically and includes your floor board as well as any floor finishes.
Ensure you have clear headroom, usually 2000mm. Loft conversions may be allowed 1900mm if you are unsure query your project with building control.
If fitted between 2 walls allow approx 10mm fitting tolerance.
If you have balustrade which passes your ceiling joist the stair width should be 50mm narrower to allow the handrail to pass plus a small gap for your fingers.