Cable Tray Fill Calculator
Free fill check for cable tray and ladder, using standard widths from the built-in Legrand-seeded manufacturer catalogue. Pick cables from the built-in library (or enter a datasheet OD), choose OD or CLEAT sizing, set your spare capacity target and get fill, spare and a suggested standard width. No login, no card.
Cables on this containment
Cable ODs are typical UK values (BS 5467 / BS 6724 style). Always verify against the manufacturer datasheet, or pick Custom OD and enter the datasheet value.
Add cables to see the fill check.
Results appear here once you add cables and a width.
That was one tray. Your project has hundreds.
FillSizer sizes every tray and ladder run on the project from your PDF floorplans and Excel cable schedule: manufacturer catalogue ODs, CPC footprint, weight vs safe working load at real support spacings, life-safety segregation and an audit-ready Excel export.
Try FillSizer free for 30 daysHow this is calculated
The calculator uses the lay-flat (side-by-side) method used in UK containment design and mirrors the FillSizer sizing engine:
- Cable width = sum of every cable's footprint: the overall diameter (OD), or in CLEAT mode the cleat width matched to that OD, multiplied by the number of conductors (single-core cables run as 2 or 4 singles) and parallel runs.
- Capacity = usable (internal) containment width, times the number of layers. A cable group (one cable, or its parallel runs and single-core conductors) lies flat in one layer, so with 2 layers the groups must also be shared out between the layers, otherwise the width fails.
- Fill = cable width ÷ capacity. Spare = what remains of the capacity.
- PASS when spare meets your target (spare exactly equal to the target passes), LOW SPARE when the cables fit with less spare than the target, FAIL when the cables physically exceed the capacity or cannot be laid in the layers.
- Suggested width is the smallest standard width whose usable capacity fits the cable width plus your spare target and whose layers hold every cable group (standard widths from the built-in Legrand-seeded catalogue: tray 50-900 mm, ladder 150-900 mm, each sized on the usable internal width shown in the size list).
What this free check does not cover
- Cable weight vs the containment's safe working load at your support spacing.
- Separate CPC (earth) cables laid alongside power cables.
- Current-rating derating for grouped or stacked cables.
- Life-safety segregation (BS 8519) and containment class rules.
- Bending radii, joints, termination space and site conditions.
The full FillSizer app checks weight, SWL, CPC and segregation against manufacturer data, per route, per floor, across the whole project.
Frequently asked questions
How is cable tray fill calculated?
Lay-flat method: the sum of every cable's footprint (OD, or cleat width in CLEAT mode, times conductors and runs), divided by the usable tray width (the internal width, which on ladder is a few millimetres less than the nominal size). Two-layer stacking gives two layers of that width, but each cable group still lies flat in one layer, so the groups must be shared out between the layers. Stacked trays should be reviewed for cable derating. This calculator applies a spare capacity target (default 25%) on top of the raw fill.
What is the difference between OD mode and CLEAT mode?
In OD mode a power cable's footprint is its overall diameter, laid side by side. In CLEAT mode, typical for cleated single runs on ladder, the footprint is the width of the cleat that holds the cable (matched by cable OD from the CMP Solace range to BS EN 61914), which is wider than the cable itself.
What spare capacity should I allow on cable containment?
A common UK design allowance is 25% spare width for future additions. Many specifications call for more. BS 8519 separately requires at least 20% spare on fire-rated supports. Set the target to match your project specification.
Where do the cable sizes and ODs come from?
The dropdown carries typical UK values (BS 5467 / BS 6724 style tables) for SWA, AWA, FP600S and common wiring cables. ODs differ between manufacturers, so verify against the datasheet for the exact cable you are specifying. You can also pick Custom OD and enter the datasheet value directly.
Does this check cable weight or safe working load?
No. This free tool checks width fill only. Weight vs the tray's safe working load at a given support spacing, CPC footprint and life-safety segregation are checked by the full FillSizer app against manufacturer catalogue data. The full app flags grouped and stacked runs for a separate current-rating (derating) review by the engineer. It does not calculate derating itself.
Disclaimer
This calculator is a preliminary design aid for qualified electrical engineers. Results are estimates based solely on your inputs. Library cable ODs are typical published values and differ between manufacturers. Verify against the datasheet for the exact cable specified. Cleat widths follow the CMP Solace range (BS EN 61914). Where no cleat covers an OD, the footprint is an estimate and an actual cleat product must be confirmed. Nominal standard widths are used. The usable width of a specific product may differ. Outputs must be independently verified by a competent person and must not be used as the sole basis for construction, procurement or safety decisions. Use of this tool is subject to the FillSizer Terms of Service.