Enter one cable size for a quick answer or build a mixed cable schedule to calculate installed fill, remaining capacity, and a suitable tray size in inches or millimeters.
The screen intentionally stops on unsupported voltage, channel tray, and size arrangements rather than extrapolating a rule.
Preset diameters are examples, not product specifications. Confirm every outside diameter against the selected manufacturer datasheet before relying on the result.
Use inside usable dimensions. Subtract dividers, covers, supports, clearances, and other unusable space before calculating.
Selected limit: -
Enter tray dimensions and a cable count.
Enter tray dimensions and cable groups to estimate fill.
Common US widths are 6, 9, 12, 18, 24, 30 and 36 inches. Metric widths use your configurable list. Manufacturer depth, usable dimensions, load classes and available ranges vary.
| Cable group | Quantity | OD | Area per cable | Total area | Projected quantity | Projected area |
|---|---|---|---|---|---|---|
| No calculation yet. | ||||||
Planning mode is a geometric estimator. NEC mode is a limited screen of supported 2014 NEC Article 392.22 cases, not a compliance determination.
area per cable = pi x outside diameter² / 4
installed cable area = sum(quantity x area per cable)
usable tray area = usable tray width x usable tray depth
installed fill % = installed cable area / usable tray area x 100
projected quantity per group = ceil(installed quantity x (1 + growth %))
projected modeled area = sum(projected quantity x cable area) x (1 + routing allowance %)
remaining allowed area = selected allowable area - projected modeled area
additional cables = floor(remaining allowed area / (additional cable area x routing factor))
Growth is rounded upward separately for every group, so a group of 1 cable with 25% growth becomes 2 cables. The routing allowance applies to the projected schedule and to each hypothetical additional cable. Additional capacity is always rounded down to a whole cable. The on-page audit shows every substitution.
| Method | What it answers | Typical input | Important limit |
|---|---|---|---|
| Geometric fill | How much of width × depth is occupied by circular cable cross-sections? | Usable dimensions, OD, count | A physical ratio, not a code allowance. |
| Project planning target | Is the schedule within a chosen spare-capacity policy? | Often 25%, 40% or 50%, plus growth | These are selectable design assumptions; none is universally NEC-compliant. |
| Code-governed allowable fill | Does a supported arrangement screen within its Article 392.22 method? | Tray construction, voltage, cable class, arrangement and size | Single vs multiconductor construction, size, layering and ventilation can change the method. |
Communications separation, cable listing, ampacity, bundling, ventilation, tray load, support span and manufacturer restrictions remain independent checks. A lower planning target can reserve access and growth, but it cannot substitute for the governing rule.
Verified rules: the screen implements the documented 2014 methods for ≤2,000 V multiconductor cables in ladder/ventilated trough or solid-bottom tray for supported small, large, mixed, and control/signal-only cases, plus supported single-layer single-conductor ranges. Planning assumptions: circular geometric area, user-selected target, growth rounding, routing allowance and standard-size list.
References: Eaton B-Line Cable Tray Manual (2014 Article 392.22 commentary and examples); NFPA 70, National Electrical Code; NEMA VE 2 cable tray installation guidance. Confirm the currently adopted edition and complete standard with the AHJ.
There is no universal NEC cable tray fill percentage. Article 392.22 changes the method with tray construction, voltage, cable class, conductor arrangement, and conductor size. The NEC screening mode covers only the supported 2014 NEC cases and is not an approval.
Multiconductor cases may use cross-sectional area limits or a single-layer width method. Supported single-conductor cases use a single-layer sum-of-diameters screen and have additional restrictions. Arrangement, conductor size, and tray type must be known.
Cable tray is a support system governed by Article 392 methods that depend on tray and cable arrangement. Conduit is a raceway with its own Chapter 9 fill rules and internal dimensions. Do not apply conduit percentages to tray or tray results to conduit.
Choose Find the required tray, enter the cable schedule and planning or supported NEC limit, then compare the passing standard sizes. Manufacturer ranges vary, so confirm usable dimensions and load rating before purchase.
Yes. The calculator floors additional capacity to a whole cable after applying the selected routing allowance to each added cable. It never reports a fractional cable.
It means the modeled installed or projected load is above the selected planning or supported NEC screening limit. Reduce the schedule, select a larger tray, or add a pathway, and have code-governed designs reviewed.
Enter inside usable width and usable loading depth after dividers, covers, supports, clearances, and unusable space. Do not use nominal outside dimensions.
No. Fill is only one check. Ampacity, derating, cable spacing, short-circuit restraint, tray load and support span, grounding, separation, firestopping, listings, and manufacturer instructions require separate verification.
Tray fill is driven by outside diameter, not pair count, AWG, or conductor count alone.
Adding tray later is usually harder than leaving spare pathway capacity during the first install.
Area fill, electrical ampacity, signal performance, grounding, and firestopping are separate validations.
Subtract dividers, side clearances, covers, supports, and any project freeboard before entering tray size.
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