Air-Core Coil Inductance Calculator

About this calculator

An air-core coil is a wound wire helix with no magnetic core material, used where core saturation, hysteresis losses, or nonlinearity would be a problem — mainly in radio-frequency circuits. Its inductance is commonly estimated with Wheeler's formula, L (µH) = (r² × N²) / (9r + 10l), where r is the coil radius in inches, N is the number of turns, and l is the coil length in inches; the formula is accurate to within about 1% for coils where length is at least 0.4 times the diameter.

RF and radio amateurs, antenna builders, and electronics hobbyists use this kind of calculation when winding tank circuit coils, RF chokes, Tesla coil secondaries, or loading coils for antennas, since air-core inductors are far more predictable and lower-loss at high frequencies than iron- or ferrite-core designs.

This calculator takes the coil's diameter, winding length, and number of turns and applies Wheeler's formula to estimate the resulting inductance, saving you from winding and re-winding a physical coil to hit a target value by trial and error.