A simple rule is that each device needs two cores—one for sending and one for receiving data. Start by counting how many devices you're connecting. The total number of cores for a 1pc fiber patch cable is calculated as the number of branches multiplied by the number of cores per branch (if there are no branches, the number of branches = 1). This guide walks you through the simple decision steps engineers use, the common strand counts on the market, and clear rules-of-thumb for different project. The number of optical cores in an optical fiber is the total number of equipment interfaces multiplied by 2, plus 10% to 20% of the spare quantity, and if the communication mode of the equipment has serial communication and equipment multiplexing, you can reduce the number of cores. Before we dive into the details, let's briefly explain. Fiber optic cables are the backbone of modern internet infrastructure, but choosing the right one can be tricky.