Air core coils are widely used in induction cooking appliances and transformers. To improve their efficiency, two characteristics are required: high combination and low loss. We propose that a litz wire using magnetoplated wires (MPWs) be used as the conductor material of a coil. Theoretical expressions for the ac resistances due to the skin and the proximity effects of air core coils using copper wires (COWs) and MPWs are derived. The calculation errors of the ac resistances of air core transformers using COWs and MPWs in the frequency range from 100 kHz to 1 MHz are 10% and 22%, respectively. The resistances of air core coils using COWs and MPWs at a frequency of 1 MHz are 43.2 mΩ and 29.2 mΩ, respectively, 34% less than of conventional air core coils.