One layer coil inductance formula permeability Air Aluminum Bismuth Carbon Steel Cobalt-Iron (high permeability strip material) Copper Ferrite (nickel zinc) Ferritic stainless steel (annealed) Iron (99.8% pure) Iron (99.95% pure Fe annealed in H) Martensitic stainless steel (annealed) Martensitic stainless steel (hardened) Nanoperm Neodymium magnet Nickel Permalloy Platinum Sapphire Superconductors Teflon Wood 1.00000037 Turns turns Wire diameter mm Length mm diameter mm