To calculate the cable tray capacity, multiply the width and height of the cable tray to find the total area, then multiply by the fill ratio. Divide this by the cross-sectional area of a single cable to find the capacity. Select Fill Standard: Choose 40% for power cables (NEC compliant) or 50% for. Calculate cable tray capacity, fill ratio, width, height, or cable diameter from four known values using inches, feet, cm, or meters. Select your tray type (ladder, ventilated trough, solid bottom, or channel), enter the tray width. This calculator determines the maximum number of cables that can be safely housed within a cable tray based on its dimensions and the cross-sectional area of the cables.