Conduit and trunking
Checks fill against your cable count and containment size.
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ACCL?
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Planning aid
Helps avoid over- or under-sized containment before ordering.
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Part of ACCL’s free suite of cost-estimating tools.
Recent projects: MF Global, Canary Wharf, Queen Elizabeth Olympic Park, Sumitomo Corporation Europe
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The calculator
Check containment capacity before you order.
💡How to use this tool: pick your containment type and size, then enter your cable mix on the left. Your fill percentage and planning-limit status update instantly on the right.
Containment type & size
Conduit
Circular
Trunking
Rectangular
Tray / basket
Open
Nominal size used as usable internal area. Deep/lidded trunking loses a little to the lid clip, so check the manufacturer datasheet for a precise figure on tight runs.
Basket tray is open containment. Depth is the standard 54mm rail unless a deep-profile tray is specified.
Cable mix: enter quantities
| Cable type | OD (mm) | Qty | Total area |
|---|
Fill guidance (editable)
Conduit max fill BICSI-aligned guidance
Trunking max fill BICSI-aligned guidance
Tray / basket max fill Open containment, more headroom
Cable area breakdown
| Cable | OD | Qty | Area |
|---|---|---|---|
| Total cable area | 0 mm² | ||
Need a containment design check?
ACCL specifies conduit, trunking and tray sizing as part of every infrastructure design, free on all survey and quotation projects.
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The editable fill percentages are practical planning defaults for telecommunications pathways, not universal statutory limits. Leaving headroom supports cable pulling, bend control, thermal performance and future additions. Conduit internal diameters and trunking/tray internal areas shown are typical figures for standard products, so confirm against the specific manufacturer's datasheet for tight or safety-critical runs. This is indicative guidance, not a substitute for a site-specific design check.
How this cable fill calculator works
Use the cable fill calculator to compare a mixed cable schedule with the usable cross-sectional area of conduit, trunking or cable tray. Select the containment type and dimensions, enter the quantity and outside diameter of each cable, and the result updates instantly.
The calculation uses the outside diameter of each circular cable to estimate its occupied area. Because cable diameters vary by manufacturer and product construction, confirm the figures against the selected cable datasheet before finalising a structured data cabling design.
The calculator supports copper data cables, coax and fibre, as well as custom cable types. This makes it useful for early route planning across office fit-outs, comms-room upgrades, security systems and fibre optic installations.
Important: the default fill percentages are editable planning values, not universal legal limits. Final containment sizing should follow the project specification, current installation standards, manufacturer data and the practical route conditions found during survey.
Why cable containment capacity matters
Overfilled conduit or trunking can increase pulling tension, compress cable bundles, make bend-radius control more difficult and leave no practical capacity for future additions. ACCL’s guide to common data cabling faults explains how overfilled containment can also contribute to damaged links and thermal problems on high-density PoE installations.
Containment should be selected around the complete cable schedule, route length, bends, draw-in points, segregation, fire stopping, manufacturer dimensions and future growth. Our office cabling service includes trunking, containment and above-ceiling or under-floor routing as part of the installation design.
For mixed copper and fibre routes, consider cable outside diameter, bend requirements and how the pathway will be accessed later. The cable category itself also affects diameter, shielding and bundle density, so review our comparison of Cat5e, Cat6, Cat6A, Cat7 and Cat8 cables when building the schedule.
The wider planning and installation principles for telecommunications pathways are covered by ISO/IEC 14763-2:2019 and, for cabling inside buildings, BS EN 50174-2:2018.
A calculation cannot confirm the actual route, internal product dimensions, existing services or installation access. ACCL’s free site survey checks these conditions before a containment design and fixed-price quotation are prepared.
Need the containment design checked?
Book a free ACCL site survey to confirm cable quantities, pathway dimensions, route constraints, future capacity and the correct conduit, trunking or tray specification.
Book Your Free Site SurveyRecent projects
Projects we have delivered.
Published case studies from ACCL’s commercial installation work.
Trading floor
MF Global, Canary Wharf
22,000 Cat6 outlets and 2,000m of 48-core fibre across four comms rooms.
Read the case study
Fibre audit and expansion
Queen Elizabeth Olympic Park
Approved network infrastructure supplier for Bring Energy, standardising fibre across 84+ buildings.
Read the case study
Live trading floor
Sumitomo Corporation Europe
Live London trading-floor infrastructure upgrade planned to avoid disruption to business operations.
Read the case studyExplore our other free calculators
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Planning containment
How the check works, and why capacity matters.
Before you book
Cable Fill Calculator FAQs
What is cable fill?
Cable fill is the proportion of the usable internal area of a conduit, trunking or cable tray that is occupied by cables. Leaving sufficient unused capacity helps with installation, cable management and future additions.
How does the cable fill calculator work?
The calculator uses the outside diameter and quantity of each cable to estimate its cross-sectional area. It then compares the combined cable area with the internal area of the selected containment.
What cable fill percentage should I use?
There is no single percentage that applies to every pathway or project. The calculator provides editable planning values, but the final allowance should follow the project specification, current installation standards, manufacturer guidance and actual site conditions.
Why should containment have spare capacity?
Spare capacity makes cables easier to install and maintain, provides room for future additions and reduces the risk of excessive pulling pressure, compressed bundles and poor thermal performance.
Can I calculate a mixture of different cable types?
Yes. You can combine Cat5e, Cat6, Cat6A, Cat7, fibre and coax cables or add a custom cable using its measured outside diameter.
Why is the cable outside diameter important?
Cables within the same category can have different outside diameters because of conductor size, shielding, jacket construction and manufacturer design. Using the selected product’s actual diameter produces a more reliable result.
Can overfilled containment affect PoE cabling?
Dense cable bundles can retain more heat, particularly where multiple cables carry higher PoE loads. Cable category, conductor size, bundle arrangement, ambient temperature and containment design should all be considered.
Do I still need a site survey?
Yes. The calculator cannot assess bends, draw-in points, segregation, fire stopping, existing services, route access or the exact internal dimensions of the selected containment. A site survey is required before the final design is confirmed.
Why businesses choose ACCL
Experienced, accountable network infrastructure specialists.
ACCL has designed and installed commercial cabling and network infrastructure since 1997, for businesses across London and the South East.
Wayne founded ACCL in 1997 and has led the delivery of commercial cabling and network infrastructure projects ever since.
Free site survey
Need the containment design checked?
Book a free ACCL site survey to confirm cable quantities, pathway dimensions, route constraints, future capacity and the correct conduit, trunking or tray specification.
- Site survey We walk the cable routes, comms rooms and access.
- Itemised quote Priced from what we saw, not a guess.
- Certified install Tested, documented and handed over.
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