Is flux density = amp x turns / length formula right, i mean how can it tell the field inside the coil if radius of the coil is UNKNOWN?

Update: Or rather field strength formular, in case someone gonna play a smartass and point that H and B are not the same (no core - core).
Update 2: u0 is assumed, you did not answer the question, what about RADIUS.
Update 3: roderick i clearly wrote which formula i am looking at and indcutance DOES depend on physical attributes.
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