This calculator uses cable sizes and tray dimensions to produce a planning estimate of fill. Practical tip: leave room for. Our free calculator helps you determine the correct tray size based on NEC and IEC standards. IEC 61537 covers cable tray and cable ladder systems for the support and accommodation of cables, while NEC Article 392 governs cable. Save your cable tray sizing calculator results as branded PDF, Excel, or Word reports with full standard references and clause numbers. Cable tray fill is the proportion of usable cross-sectional area inside a cable tray occupied by installed cables. 5 inches, in a 4-inch deep cable tray.