NEC Chapter 9 Conduit Fill
How Many Wires Fit in 1-1/4" IMC?
The maximum THHN conductors per wire size in 1-1/4 inch IMC (IMC (intermediate metal conduit)) at the NEC 40% fill limit, with the math and the interactive calculator for any mix of wires.
Max THHN Conductors in 1-1/4" IMC (40% Fill)
Maximum number of same-size THHN/THWN-2 conductors in 1-1/4 inch IMC at the NEC Chapter 9 40% fill limit. Count the equipment ground as a conductor.
| Wire Size (THHN) | Max Conductors | Area Each (sq in) |
|---|---|---|
| #14 AWG | 68 | 0.0097 |
| #12 AWG | 49 | 0.0133 |
| #10 AWG | 31 | 0.0211 |
| #8 AWG | 18 | 0.0366 |
| #6 AWG | 13 | 0.0507 |
| #4 AWG | 8 | 0.0824 |
Based on 1-1/4 inch IMC internal area 1.647 sq in (NEC Chapter 9 Table 4). One conductor allows 53% fill, two allow 31%, three or more allow 40% (Table 1).
Mixed Wire Sizes? Calculate It
The chart is for one wire size at a time. For a real pull with mixed sizes, insulation types, or other conduit, enter your exact conductors for the precise fill percentage.
Frequently Asked Questions
How many wires fit in 1-1/4 inch IMC?
At the NEC 40% fill limit for three or more conductors, 1-1/4 inch IMC (internal area 1.647 sq in) holds 49 #12 THHN, 68 #14, 31 #10, or 18 #8 conductors. The math is the conduit area times 0.40 (1.647 × 0.40 = 0.659 sq in allowable), divided by the conductor's area from NEC Chapter 9 Table 5.
How many 12 AWG THHN wires fit in 1-1/4 inch IMC?
49 #12 THHN conductors fit in 1-1/4 inch IMC at the 40% fill limit. Each #12 THHN is 0.0133 sq in, so 0.659 sq in allowable ÷ 0.0133 rounds to 49 conductors (NEC Chapter 9 Note 7 rounds up when the decimal is 0.8 or more). The same count applies to THWN-2, which has the identical area.
How many #10 THHN wires fit in 1-1/4 inch IMC?
31 #10 THHN conductors fit in 1-1/4 inch IMC at the NEC 40% fill limit. Each #10 THHN is 0.0211 sq in, so 0.659 sq in allowable (1.647 × 0.40) ÷ 0.0211 rounds to 31 conductors (NEC Chapter 9 Note 7). THWN-2 has the identical area and gives the same count. Count the equipment ground as a conductor.
How many 14 AWG wires fit in 1-1/4 inch IMC?
68 #14 THHN conductors fit in 1-1/4 inch IMC at 40% fill. Each #14 THHN is 0.0097 sq in, so 0.659 sq in ÷ 0.0097 rounds to 68 (NEC Chapter 9 Note 7). Remember the ground counts as a conductor, and more than three current-carrying conductors trigger ampacity derating per NEC 310.15(C)(1).
What is the fill limit for 1-1/4 inch IMC?
The maximum fill depends on how many conductors are in the raceway (NEC Chapter 9, Table 1): 53% for one conductor, 31% for two, and 40% for three or more. For 1-1/4 inch IMC (internal area 1.647 sq in, IMC (intermediate metal conduit)) that is 0.873 sq in for one wire, 0.511 sq in for two, and 0.659 sq in for three or more. The 40% case is the common one.
Fill for Other IMC Sizes
Wires in 1/2" IMC
10 #12 THHN and the full count for 1/2 inch pipe.
Wires in 3/4" IMC
17 #12 THHN and the full count for 3/4 inch pipe.
Wires in 1" IMC
29 #12 THHN and the full count for 1 inch pipe.
Wires in 1-1/2" IMC
67 #12 THHN and the full count for 1-1/2 inch pipe.
Wires in 2" IMC
109 #12 THHN and the full count for 2 inch pipe.
Wires in 2-1/2" IMC
154 #12 THHN and the full count for 2-1/2 inch pipe.
Wires in 3" IMC
238 #12 THHN and the full count for 3 inch pipe.
Wires in 3-1/2" IMC
318 #12 THHN and the full count for 3-1/2 inch pipe.
Wires in 4" IMC
410 #12 THHN and the full count for 4 inch pipe.
1-1/4" in Other Conduit Types
The same 1-1/4 inch trade size holds a different number of wires depending on the conduit type, because each has a different internal area (NEC Chapter 9 Table 4).
Fill checks out. Will the wire reach?
Getting the conductors in the pipe is one thing. Confirm the gauge holds up over distance with the voltage drop calculator before you pull.