The following formula is used to calculate the cable tray capacity: Variables: 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. This weight is always there once the cables are in. Big cables weigh more: Thicker cables with more conductors mean more material, so they are heavier. Snow Load (S):. Load capacity is not just about how much weight the tray can physically support; it also involves maintaining proper fill percentages, ensuring adequate airflow, preventing ampacity derating, and preserving electrical safety through proper grounding and bonding. Dynamic load (Live Load): additional loads that may arise during construction and maintenance, such as personnel walking.