What size cable tray do I need for my cables? Calculate the appropriate cable tray size based on your cables and fill requirements. In practice, cable tray dimensions are a system of interrelated measurements —width, depth, length, and material thickness—that directly affect cable fill compliance, heat dissipation, structural loading, and long-term expandability. Common widths include 100mm, 200mm, 300mm, and 450mm. Below are industry-standard tray and ladder.