Conduit Fill Calculator

Calculate conduit fill percentage per NEC Chapter 9 Table 1. Select conduit and add cables to check compliance.

Fill

4.2%

Max Allowed

53%

Cables

1

Status

PASS
Conduit

Internal area: 0.864 sq in

Cables
Add cables to calculate fill
Fill Analysis
Fill: 4.2%Max: 53%
0%50%100%
Conduit area0.864 sq in
Cable area used0.036 sq in
Allowable area (53%)0.458 sq in
Remaining0.422 sq in
NEC Fill Rules

1 cable: 53% max fill

2 cables: 31% max fill

3+ cables: 40% max fill

Based on NEC Chapter 9, Table 1

Cable Breakdown
Cat5e x10.036 sq in
What is Conduit Fill?

Conduit fill calculation determines what percentage of a conduit's internal cross-sectional area is occupied by cables. The National Electrical Code (NEC) Chapter 9, Table 1 sets maximum fill percentages to prevent overheating, allow heat dissipation, and leave room for pulling additional cables in future.

How to use this calculator:

  1. Select your conduit type (EMT, IMC, PVC, etc.) and trade size
  2. Add cables from the predefined AV cable types, or enter custom cable dimensions
  3. The fill bar shows whether your cable bundle meets NEC requirements
  4. Toggle between imperial and metric units as needed

Tip: Always use the cable's listed outer diameter (OD), not the conductor size. Account for all cables in the conduit — power, data, and signal. Aim for 30% fill even though 40% is the NEC maximum for 3+ cables, to leave room for future additions and easier pulling.