Cable tray fill calculator
Enter the cables you are running and the tray you are considering. It returns the fill percentage, whether they sit in a single layer, and the narrowest width we roll that keeps you under 40%.
Tray size
Cables
Overall outside diameter, not conductor size. It is printed on the cable datasheet.
Result
18.3% fill. Within the 40% figure most specifications work to.
- Cables
- 18
- Occupied area
- 4,128 mm²
- Tray cross-section
- 22,500 mm² (300 × 75)
- Sum of diameters
- 300 mm vs 300 mm width
- Single layer?
- Yes, they sit side by side
This is a sizing aid, not a compliance check. It works out geometry only. It does not tell you whether the tray carries the weight: safe working load depends on the section, the support span and the load class under IEC 61537, and it has to come from the load table for the specific tray. Where NEC 392.22 applies, its tabulated limits govern rather than the 40% figure used here.
Send this spec and get the load tableFill is geometry, and you can check it by hand
There is nothing proprietary in this calculation, which is why it is worth showing rather than hiding behind an enquiry form.
Occupied area
Each cable is treated as a circle: area is πd²/4 from the overall outside diameter, then multiplied by how many of that size you are running. Use the O.D. printed on the cable datasheet, not the conductor cross-section in mm².
Tray cross-section
Width multiplied by usable depth. Usable depth is not always the rail height. If the specification calls for a cover, or the run carries a separation barrier, the space available to cables is less than the rail suggests.
The 40% figure
Widely used in practice, but it is a convention rather than a universal code limit. Where NEC 392.22 applies it gives its own tabulated allowances, and IEC 61537 classifies trays by load rather than by fill at all. Follow the project specification where the two disagree.
It will not tell you the tray holds the weight
Fill and load are different questions, and conflating them is the most common sizing mistake we see on incoming enquiries.
A 300 mm tray at 30% fill can still be over its safe working load if the cables are heavy and the supports are far apart. Safe working load depends on the section profile, the material and thickness, and above all the support span. Under IEC 61537 a tray is classified by the load it carries over a stated span, which is why two trays of identical width can carry very different loads.
That figure has to come from the load table for the specific tray. We publish ours on request with the section drawing, so you can check the span against your support spacing before anything is ordered.
See the cable tray range · Ladder or perforated? · Using tray as an equipment grounding conductor
Send the cable schedule, get the tray schedule back.
Give us the cable list and support spacing and you will get widths, depths, load class and the section drawing, from the people who roll the tray.
- MTC · COO · inspection reports
- ±0.01 mm precision · in-house QA
- FOB · CIF · CFR to all major ports