Cable trays and conduits are evaluated by comparing the total cross-sectional area of installed cables against the available area.
Fill percentage is computed as:
F = 100 × Σ Acable / Aspace
Where Acable is the area of each cable and Aspace is the usable area of the tray or conduit. The tool follows NEC guidance: conduits are typically limited to 40% fill and cable trays to 50% unless noted otherwise.