Conduit Fill Calculator

Conduit Fill for AV Installations

Running AV cables through conduit is a best practice for clean, professional installations and future-proofing your home or commercial space. However, stuffing too many cables into a conduit makes pulling difficult, risks cable damage, and can cause heat buildup that degrades signal quality. The National Electrical Code (NEC) Chapter 9 sets clear limits on how full a conduit can be.

The NEC specifies three fill thresholds: 53% for a single cable, 31% for two cables, and 40% for three or more cables. These percentages refer to the ratio of total cable cross-sectional area to the internal area of the conduit. For most AV runs you will be pulling three or more cables, so 40% is the practical limit to remember.

When planning conduit runs for home theaters, media rooms, or whole-house audio/video distribution, always plan for future expansion. A good rule of thumb is to size your conduit so it is only 30% full at initial installation, leaving room to add cables later. Pair this calculator with our Speaker Wire Gauge Calculator to choose the right wire and our Voltage Drop Calculator to ensure your low-voltage wiring performs correctly over long runs.