Abstract: The self-inductance sensor disclosed includes a band of distensible material, and a strap of nondistensible material which form in combination a closed loop which circumscribes the object. A conductor is secured to the band of distensible material. The conductor includes two portions each extending from one end of the band to the other and having an irregular repetitive configuration. The conductor portions are symmetrically juxtaposed to one another to form a series of substantially enclosed areas which change shape as the band is distended. The self-inductance of the conductor is measured to indicate the relative extension of the band and thus the change in circumference of the object.