Field produced inside a toroid

Consider a toroid (similar to a ring) wound uniformly with N turns.
If the mean radius of the magnetic path of the toroid is a, then
the magnetic path length would be (2πa)  and the total mmf
produced would be N I.
Thus from Ampere’s Law
magnetic field

                 H=NI/2πa

inside the toroid. [variation of the magnetic field inside the cross
section of the toroid is usually not necessary to be considered and is assumed uniform].