Cable Tray Fill Calculator
Calculate cable tray fill percentage and remaining capacity from tray dimensions and a list of cable diameters, checked against a configurable fill limit.
Input
Internal usable width of the cable tray.
Internal usable (loading) depth of the cable tray.
Maximum allowed cross-sectional fill, per your applicable code or design standard.
Outer diameter in mm, optionally followed by a quantity (default 1). E.g. "25,4" = four 25 mm cables.
Output
| Quantity | Value |
|---|---|
| No data yet | |
Guides
Overfilling a cable tray traps heat and makes future cable pulls impossible; underfilling wastes tray real estate you already paid for. This calculator adds up the cross-sectional area of every cable you're routing and checks it against your tray's usable area and a configurable fill limit.
How to use it
- Enter the tray's internal width and depth in mm — the usable cross-section, not the outer frame dimensions.
- Set the fill limit — the maximum percentage of that area your design standard allows. 40% is a common general-purpose figure; check your applicable electrical code for the specific case.
- List your cables, one line per size: diameter in mm, optionally followed by a comma and a quantity (e.g.
25,4for four 25 mm cables). Leave the quantity off for a single cable.
The tool totals the cable count and cross-sectional area, computes the fill percentage, and reports whether it's within your limit — with either the remaining capacity or the overfill amount.
The formula
- Cable area =
Σ (quantity × π × (diameter ÷ 2)²) - Tray area =
width × depth - Fill % =
cable area ÷ tray area × 100
This is the general cross-sectional-area fill method. It's a simplified, code-agnostic approximation — some electrical codes (e.g. NEC 392.22) use a separate diameter-sum method specifically for single-conductor cables in ladder or ventilated trays, which this calculator doesn't model. Always verify against the electrical code that applies to your installation.
Why does fill percentage matter?
Cables generate heat under load, and a densely packed tray traps that heat instead of letting it dissipate — pushing conductors toward their thermal limits faster than an open tray would. A lower fill percentage also leaves room to add cables later without re-pulling the whole tray.
What fill limit should I use?
It depends on the tray type, cable type, and applicable code — common general guidance sits between 30% and 50%. Check your local electrical code or engineering standard rather than assuming a single number applies everywhere.
Privacy
Everything is calculated in your browser. No values are sent to a server.
Related tools
To size the feeder wires going into the tray, use the Wire Size Calculator. For the transformer feeding those circuits, see the Transformer Sizing Calculator.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/cable-tray-fill-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"trayWidth": "300",
"trayDepth": "100",
"fillLimit": "40",
"cables": "25,4\n40,2\n18,6"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `cable-tray-fill-calculator` tool (Cable Tray Fill Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.