This site offers many simple-to-use calculators and wire ampacity charts to aide you in properly sizing wire and conduit in compliance with the NEC. Calculate proper wire gauge, voltage drop, and ampacity for safe electrical installations. Whether you are installing outlets, switches, lighting fixtures, or junction connections, box size directly affects wire fill capacity, device fit, and installation quality. Why Use Our Wire Size Calculator? Calculations follow National Electrical Code standards for safe. The following step-by-step guide will show you how to calculate the correct size of cable and wire, or any other conductor, for electrical wiring installations with solved examples in both British or English and SI Systems, i.