How Many Wires Fit in Conduit? EMT and PVC Fill Chart

A 3/4 inch EMT holds up to 16 wires of 12 AWG THHN, and a 1/2 inch EMT holds 9. The limit comes from the National Electrical Code, which lets the wires fill only 40% of the inside of the conduit when there are three or more of them. The conduit fill calculator works out the fill for your own mix of conduit and wire, including a ground wire of another size.

Wires allowed in EMT

Most THHN or THWN-2 wires of one size, by trade size. The ground wire counts as one of them.

Wires allowed in PVC Schedule 40

PVC Schedule 40 has a thicker wall than EMT, so it holds slightly fewer wires of the same trade size.

Bigger conduit

EMT, for the larger sizes used for feeders:

Which conduit for a common job?

The smallest conduit for the wires in a common job, counting the ground:

These are the sizes for fill only. Check the wire gauge for the load with the wire size calculator first.

The rules behind the chart

• 40% for three or more wires, 31% for two, 53% for one. These are the limits in NEC Chapter 9, Table 1. The wires need room so that they can be pulled and so that the heat can get away.
• The area of the wire includes its insulation. A 12 AWG THHN wire takes 0.0133 square inches. The conduit areas are in Table 4 and the wire areas in Table 5.
• Same-size wires round up. When every wire is the same size, a result of 0.8 or more above a whole number may be rounded up. That is why 3/4 inch EMT holds 6 wires of 8 AWG even though 5.8 would fit by area.
• Mixed sizes add up by area. Three 12 AWG wires and a 10 AWG ground add up to 0.0610 square inches, which is 20.1% of a 1/2 inch EMT, and there is room for 7 such wires.
• Short nipples may be fuller. A conduit nipple of 24 inches or less may be filled to 60%.
• Only the wire types in the table. The areas are for THHN, THHW and THWN-2. Other insulation types such as XHHW are thicker. Romex (NM-B) cable is a different product and is not counted this way.

Fill is not the only limit

• Heat. More than three current-carrying wires in a conduit lower the ampacity of every wire (NEC 310.15). Four to six current-carrying wires are derated to 80%, and seven to nine to 70%. A conduit that is physically large enough may still need larger wire.
• Pulling. A long run or several bends make a full conduit hard to pull. Stay near 30% fill if you can, and use wire lubricant.
• Bends. No more than 360 degrees of bends (four 90 degree bends) are allowed between pull points. Put a pull box in a long run.
• Future circuits. A size up costs little. Adding a circuit to a full conduit means pulling everything again.

Worked example

You want to pull nine wires of 12 AWG THHN (no separate ground) in a 1/2 inch EMT. The wires cover 0.1197 square inches of the conduit, which is 39.4% and just under the 40% limit, so that is the most the conduit will take. A tenth wire does not fit, and you would need 3/4 inch EMT. Our own run of six wires and a ground in 3/4 inch EMT is 17.5% full.

Estimates only: the NEC and your local code are the rule, and your inspector decides. Have an electrician look at any work on the service or the panel.

Frequently asked questions