Estimate duct utilization for single or mixed cables. Select units, packing, and target fill ratio. Download CSV and PDF summaries for teams and clients.
| Scenario | Duct | Cables | Fill limit | Packing | Reserve | Expected outcome |
|---|---|---|---|---|---|---|
| Urban handhole run | Circular ID 100 mm, clearance 2 mm | 6 × OD 12 mm | 40% | 0.85 | 10% | PASS with moderate spare area |
| Campus backbone pull | Circular ID 63 mm, clearance 1 mm | 2 × OD 18 mm | 31% | 0.82 | 0% | Check carefully; near limit in practice |
| Mixed drop bundle | Rectangular 60×40 mm, clearance 1 mm | 8 × 10×6 mm, plus 4 × OD 8 mm | 40% | 0.80 | 5% | May FAIL; consider larger duct |
Fiber duct capacity is more than a geometric check; it supports constructability, pull safety, and lifecycle growth. In congested corridors, accurate capacity planning reduces rework, avoids mid-pull stoppages, and improves schedule reliability. This calculator converts duct and cable dimensions into comparable areas, then applies practical allowances so planning outputs align with field realities.
Conduit fill limits are commonly applied to control friction, heat, and installation difficulty. The auto option follows widely used planning ratios for one, two, and three-or-more cables. For owner standards or project specifications, the custom limit lets you enforce a required maximum occupancy and keep designs consistent across packages.
Packing factor represents how efficiently cables can occupy the available space during pulling and placement. Values between 0.75 and 0.93 are typical for planning, depending on cable stiffness, bundle control, and pull length. Reserve percent protects future expansions, minimizes operational risk, and helps avoid “design-to-the-limit” congestion.
Real projects often mix backbone, feeder, and drop cables in the same duct route. The mixed mode sums the total cable area across up to three cable types and compares it to the allowed occupied area. The planning add-on badges estimate how many additional cables of a given type could be added before exceeding the defined limit.
Use this reference case to verify inputs and interpretation: Circular duct ID 100 mm, clearance 2 mm; 6 cables at OD 12 mm; fill limit 40%; packing 0.85; reserve 10%. The expected result is a PASS with measurable spare area for future work orders.
| Input | Value |
|---|---|
| Duct | Circular ID 100 mm |
| Clearance | 2 mm |
| Cable set | 6 × OD 12 mm |
| Fill / Packing / Reserve | 40% / 0.85 / 10% |
Use inner dimensions (ID/inner width and height). Capacity is based on usable space, not outside wall dimensions.
It reduces theoretical area to reflect real-world inefficiency from cable stiffness, bundling, and imperfect packing during pulls.
Use custom when owner standards, local codes, or project specs mandate a specific maximum fill percentage for design approval.
Clearance models practical setbacks from walls, couplers, and installation tolerances so the usable area is not overstated.
Apply a reserve percent to hold space for later adds. It prevents reaching the limit on day one and supports phased buildouts.
No. PASS indicates area compliance only. Pull length, bends, lubricant, conduit condition, and cable jacket friction still affect installability.
Enter outer jacket dimensions. For irregular profiles, use manufacturer maximum OD or major/minor axes to maintain conservative results.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.