Ferrite and powdered-iron cores carry a published AL and a tolerance that is often ±20%. Quoting a single inductance figure hides that — this shows the range you will actually get.
Turns for common ferrite and powdered-iron cores — with the tolerance shown.
Toroid cores carry a published inductance-per-turn (the “AL” value) that often varies plus-or-minus 20% part to part.
Because AL varies, treat the number as a starting point and measure the finished part for anything resonant.
