What we have: A 100-foot cable tray section. Don't forget the weight of any lids or dividers. Estimate physical weight of ladder, perforated, solid-bottom, and wire mesh trays using material density, length, and dimensions. Calculate theoretical structural tray weights using dimensions, length, material composition, and custom density parameters. Results are. What Puts Weight on Your Cable Trays? Before we dive into the numbers, let's look at what actually adds weight to a cable tray. Fill percentage is checked from cable outside diameter so you can compare cross-sectional packing against side rail depth.