Selecting the correct wire size for a given ampacity is the most fundamental step in electrical circuit design. NEC Table 310.16 sets the allowable ampacities for conductors in a raceway at 30°C ambient — but real installations often require derating for elevated ambient temperatures, bundling of multiple conductors, or continuous loads (which require a conductor rated at 125% of the load). This tool performs the full NEC 310.16 lookup and applies all required derating factors automatically. Enter your load in amps, continuous or non-continuous load type, conductor material, and installation conditions to get the minimum wire size that meets NEC requirements.
45A continuous load requires minimum ampacity of 45 × 1.25 = 56.25A. From NEC Table 310.16, 75°C column: 6 AWG copper = 65A. Selected: 6 AWG copper.
This is a variant of the full Wire Size Calculator — which supports all wire materials, derating factors, and load types in a single tool.
Try all options in the full Wire Size Calculator →