The thickness of a fiber optic cable can be determined by the following criteria: Use (Indoor, Outdoor): Outdoor cables tend to have thicker protective layers as they are exposed to weather, moisture, and physical stress. Indoor cables, on the other hand, are usually thinner and. Choosing the right fiber size depends on application type, environment (indoor/outdoor), and connector compatibility. Using a fiber size chart simplifies cable selection and ensures compliance with industry standards (TIA, ISO, ITU-T). Geometric measurements are used to determine the physical properties of the fiber. The outside diameter of typical fibers is about 125 11m, or about the thickness of a piece of paper.