How to Calculate Conduit Fill
Conduit fill is the amount of a conduit’s cross-sectional area that is occupied by a cable or cables,
based on the cable outside diameter and the conduit inside diameter. In practice, it is limited as a
ratio, typically expressed as a percentage, and enforced by code, standard, or best practice to help
assure system safety and performance. The ratio can be used to determine appropriate conduit size or
determine how many cables can be placed in an existing conduit.
The maximum recommended ratio can be affected by several factors, including application type, number of cables in the conduit, and the number of conduit bends. The following table provides maximum recommended fill for many standard conduit sizes at the maximum fill ratio specified by the United States National Electrical Code (NEC) for domains within its scope. This also assumes no more than two 90° bends between pull points. Guidance is also provided below on how to calculate conduit fill. Other codes, standards or practices may dictate other maximum fill ratios, but the methodology remains the same.
How to Calculate Conduit Fill-Sizing a Conduit
