The diameter of wires is measured by a standard reference number referred to as the American Wire Gauge (AWG). Figure 4-4 lists some gauge values and the equivalent diameter. From the diameter and assuming copper wire, we can estimate the resistance per length. For example, 22-gauge wire, typical in many personal computer boxes, has a diameter of 25 mils. Its resistance per length is RL = 1.58 μOhm-cm/( 2.54 cm/ inch)/( π/ 4 × 25 mil2) = 1.2