Size the tray by calculating total cable cross-sectional area and dividing by the allowable fill percentage (typically 40%). Add 20–30% spare capacity for future cables. Standard tray widths are 6, 9, 12, 18, 24, and 30 inches. Our free calculator helps you determine the correct tray size based on NEC and IEC standards. Follow these simple steps: Define Tray Dimensions: Enter the width and depth of your planned cable tray (in mm or inches). IEC 61537 covers cable tray and cable ladder systems for the support and accommodation of cables, while NEC Article 392 governs cable. Our cable tray fill calculator is designers to compute the appropriate size and capacity of cable trays. In complex engineering environments, the.