3-1/2 Inch Conduit Fill Chart

Q: How many #12 THHN wires fit in 3-1/2" conduit?

Up to undefined #12 THHN wires fit in 3-1/2" EMT conduit per NEC Chapter 9 Table C1, based on 40% fill for 3+ conductors.

Q: What is the fill area of 3-1/2" EMT conduit?

3-1/2" EMT conduit has an internal area of 2.876 sq inches. At 40% fill (3+ wires): 1.15 sq inches available. At 31% fill (over 2 wires): 0.891 sq inches.

Q: What are the NEC conduit fill rules?

1 wire: 53% fill. 2 wires: 31% fill. 3+ wires: 40% fill per NEC Chapter 9 Table 1. These percentages apply to the conduit internal cross-sectional area.

How many wires fit in 3-1/2" conduit? See the complete THHN wire fill chart for 3-1/2" EMT, PVC, and rigid conduit per NEC Chapter 9 Table C1. Common uses: Large commercial feeders.

3-1/2" Conduit Specifications

3-1/2" (3.5" trade size)

EMT Area

2.876 sq in

PVC Area

2.99 sq in

40% Fill

1.15 sq in

31% Fill

0.891 sq in

Common Use

Large commercial feeders

THHN Wire Fill Chart — 3-1/2" EMT Conduit

Wire Size	Max Wires (40% fill)
#2 THHN	28 wires
#4 THHN	38 wires
#6 THHN	55 wires
#8 THHN	77 wires
#1/0 THHN	19 wires
#2/0 THHN	16 wires

Based on NEC Chapter 9 Table C1 for EMT conduit with THHN/THWN-2 conductors at 40% fill (3+ conductors).

NEC Conduit Fill Rules

1 conductor: 53% of conduit area. 2 conductors: 31% of conduit area. 3+ conductors: 40% of conduit area. These rules are per NEC Chapter 9 Table 1 and apply to all conduit types (EMT, PVC, rigid).

Equipment grounding conductors count toward fill but not toward ampacity derating. Bare grounds use less area than insulated conductors of the same gauge.

When to Use 3-1/2" Conduit

Large commercial feeders. This is a commercial/industrial size for large feeders and service entrance conductors. Use our Conduit Fill Calculator for exact fill calculations with mixed wire sizes.

Disclaimer: Based on NEC Chapter 9 tables. Verify with local codes. Consult a licensed electrician.