Electrical Conduit Fill Capacity

Direct Answer

Electrical conduit fill capacity is strictly regulated under the National Electrical Code (NEC Chapter 9, Tables 1, 4, and 5) limiting total conductor cross-sectional area to 40% of internal conduit area for three or more wires, preventing heat buildup and insulation damage during wire pulls.

Source: NFPA 70: National Electrical Code (NEC) Chapter 9, Tables 1, 4 & 5 / NEMA TC 2 · Last reviewed Aug 28, 2026

Specs

Governing Standards	NFPA 70 (NEC) Chapter 9 / Annex C (Conduit Fill Tables) / NEMA Standards
The NEC 40% Fill Rule	1 Conductor: 53% max \| 2 Conductors: 31% max \| 3 or More Conductors: 40% max cross-sectional fill
1/2" EMT Conduit (Trade Size 16)	Internal Area: 0.304 sq in \| 40% Fill: 0.122 sq in \| Max 9× 14 AWG, 6× 12 AWG, or 4× 10 AWG THHN wires
3/4" EMT Conduit (Trade Size 21)	Internal Area: 0.533 sq in \| 40% Fill: 0.213 sq in \| Max 16× 14 AWG, 10× 12 AWG, or 7× 10 AWG THHN wires
1" EMT Conduit (Trade Size 27)	Internal Area: 0.864 sq in \| 40% Fill: 0.346 sq in \| Max 26× 14 AWG, 16× 12 AWG, or 12× 10 AWG THHN wires
1-1/4" EMT Conduit	Internal Area: 1.496 sq in \| 40% Fill: 0.598 sq in \| Ideal for 100A subpanel feeds (3× 1 AWG + 6 AWG ground)
2" EMT Conduit	Internal Area: 3.356 sq in \| 40% Fill: 1.342 sq in \| Standard 200A residential service mast (3× 2/0 Cu or 4/0 Al)
Conduit Types	EMT (Electrical Metallic Tubing), Schedule 40 PVC, Schedule 80 PVC (Thick wall), Rigid Metal (RMC)

NEC Maximum Number of THHN / THWN Conductors in EMT Conduit (Table C.1)

Conductor Wire Gauge (AWG)	Conductor Area (sq in)	1/2" EMT (40% Fill: 0.122 in²)	3/4" EMT (40% Fill: 0.213 in²)	1" EMT (40% Fill: 0.346 in²)	1-1/4" EMT (40% Fill: 0.598 in²)	2" EMT (40% Fill: 1.342 in²)
14 AWG THHN	0.0097 in²	9 Wires	16 Wires	26 Wires	45 Wires	101 Wires
12 AWG THHN	0.0133 in²	6 Wires	10 Wires	16 Wires	28 Wires	63 Wires
10 AWG THHN	0.0211 in²	4 Wires	7 Wires	12 Wires	20 Wires	46 Wires
8 AWG THHN	0.0366 in²	2 Wires	4 Wires	6 Wires	11 Wires	25 Wires
6 AWG THHN	0.0507 in²	1 Wire	3 Wires	4 Wires	8 Wires	18 Wires
4 AWG THHN	0.0824 in²	1 Wire	1 Wire	2 Wires	5 Wires	11 Wires
2 AWG THHN	0.1158 in²	1 Wire	1 Wire	1 Wire	3 Wires	8 Wires
2/0 AWG THHN	0.2223 in²	0	0	1 Wire	1 Wire	4 Wires (200A Feed)
4/0 AWG Aluminum	0.3278 in²	0	0	0	1 Wire	3 Wires (200A Main)

Ampacity Derating for More Than 3 Current-Carrying Conductors (NEC 310.15)

While a 3/4" EMT conduit physically fits 16 individual 14 AWG wires under the 40% area rule, NEC Table 310.15(C)(1) mandates derating wire ampacity when bundling current-carrying conductors:

4 to 6 conductors: Derate to 80% of base ampacity.
7 to 9 conductors: Derate to 70%.
10 to 20 conductors: Derate to 50% (a 20A #12 wire drops to only 15A rating).
Rule of Thumb: Run multiple conduit branches or upsize wire gauge when pulling more than 3 active circuits.