Use a conduit wire capacity chart by finding the size and type of the conduit and the size of the wire, and then finding the cell on the chart where these values intersect. The value in the intersecting cell is the maximum number of wires that conduit can accommodate.
Most conduit wire capacity charts list the conduit sizes in the leftmost column. Typically, wire capacity charts list conduits of between 0.5 and 4 inches in length. The next row to the right lists the type of conduit according to its construction material. Charts list the different sizes of wires by increasing gauge number in the uppermost row.
The values in the chart's main body represent the number of wires any given conduit can hold. For instance, a 2-inch intermediate metal conduit can hold nine number-2 wires, 39 number-8 wires or 109 number-12 wires, aside from several other capacities.
There are four common conduit types: polyvinyl chloride, galvanized rigid steel, intermediate metal and electrical metallic tubing. Polyvinyl chloride, also known as PVC or plastic tubing, is the most affordable and lightest conduit type, but it also has the lowest capacity. Each of the three metal conduit types has similar performance, but intermediate metal generally has the highest wire capacity.