Fully implantable biosensors require small size to be minimally invasive. To avoid embedded batteries, power can be supplied by means of printed spiral inductors located on the skin, close to the implanted devices. Reliable models are required to optimize the design of such inductors. In this paper, a RLC model to describe the electrical properties of printed spiral inductors is proposed. The model is based on the geometrical and physical characteristics of the inductors. The accuracy of the model is finally compared with the experimental measurements.