Number of cables in enclosed pathways meeting maximum fill ratio criteria

Enter cable diameter and pathway (conduit) internal diameter. Results use standard industry fill factors: 53% (one cable), 31% (two cables), 40% (three+ cables).

Cable ∅ (Dc): mm
Pathway ∅ (Dp): mm
1 cable2 cables3+ cables
F, standard: 53%31%40%
N, rounded up:
F, actual:
N, rounded down:
F, actual:

Cable ∅ (Dc): in
Pathway ∅ (Dp): in
1 cable2 cables3+ cables
F, standard: 53%31%40%
N, rounded up:
F, actual:
N, rounded down:
F, actual:

Note: Results assume circular pathway and identical round cables. Actual install capacity can vary with pulling geometry, bends, and spacers.

Solid Conductor Gauge

AWG Conductor diameter Conductor area Weight DC resistance (20°C)
mmin mm²kcmil kg/mlb/ft Ohm/mOhm/ft

Enter any one of: AWG, diameter (mm or in), or area (mm² / kcmil). The rest will auto-calc.

Enclosed Cable Pathway Fill — Explanation

An enclosed cable pathway is a cable pathway whose contents are accessed at the ends or by removing a cover/lid, fully surrounding the cables.

Types of enclosed pathways

  1. Without longitudinal access (“end-access”; e.g., conduit).
  2. With longitudinal access (“length-access”; with hinged or removable lid/cover).

Fill ratio definition

The pathway fill ratio \(F\) expresses how much of the pathway’s cross-section is occupied by cables (ignores interstitial gaps and bends):

\[ F \;=\; \frac{\text{Integrated cross-sectional area of all cables}}{\text{Cross-sectional area of pathway internal space}} \]

Symbols:

  • \(F\) = pathway fill ratio
  • \(D_c\) = cable diameter; \(N\) = number of identical cables
  • \(A_c = \tfrac{\pi D_c^{2}}{4}\) = area of one round cable
  • \(A_p\) = cross-sectional area of pathway internal space

Pathway cross-section

  • Circular: \(\displaystyle A_p = \frac{\pi D_p^{2}}{4}\) where \(D_p\) is the internal diameter.
  • Rectangular: \(\displaystyle A_p = H \times W\) where \(H\) and \(W\) are internal height and width.

Simplified (identical round cables in circular pathway)

\[ F \;=\; N \left( \frac{D_c}{D_p} \right)^{2} \]

Industry standard fill factors

  • 1 cable: \(53\%\)
  • 2 cables: \(31\%\)
  • 3+ cables: \(40\%\)

Reverse calculation — maximum number of cables

  • Circular pathway: \[ N \;=\; F \,\frac{D_p^{2}}{D_c^{2}} \]
  • Rectangular pathway: \[ N \;=\; F \,\frac{H\,W}{\frac{\pi D_c^{2}}{4}} \;=\; \frac{4FHW}{\pi D_c^{2}} \]

Rounding guidance

  • For small counts (≤3), rounding up can be unrealistic (e.g., summed cable diameters exceeding \(D_p\)).
  • Always verify rounded values against the target fill factor.
  • Higher counts better correlate with the target \(F\); rounding down is the conservative choice.

These formulas assume straight runs, identical round cables, and circular or rectangular pathways.