Cable tray fill is a way to estimate how much space cables take up inside a tray, often expressed as a percentage. This calculator uses cable sizes and tray dimensions to produce a planning estimate of fill. In EPC and industrial automation projects, a tray that is undersized forces last-minute redesigns, cable overcrowding, poor heat. Our free calculator helps you determine the correct tray size based on NEC and IEC standards. Select Fill Standard: Choose 40% for power cables (NEC compliant) or 50% for. Cable tray types, fill rules for single-conductor and multiconductor cables, ampacity derating, separation requirements, and when to use tray vs conduit.