NEC Chapter 9 Conduit Fill
How Many Wires Fit in 1/2" RMC?
The maximum THHN conductors per wire size in 1/2 inch RMC (RMC (rigid metal conduit)) at the NEC 40% fill limit, with the math and the interactive calculator for any mix of wires.
Max THHN Conductors in 1/2" RMC (40% Fill)
Maximum number of same-size THHN/THWN-2 conductors in 1/2 inch RMC 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 | 13 | 0.0097 |
| #12 AWG | 9 | 0.0133 |
| #10 AWG | 6 | 0.0211 |
| #8 AWG | 3 | 0.0366 |
| #6 AWG | 2 | 0.0507 |
| #4 AWG | 1 | 0.0824 |
Based on 1/2 inch RMC internal area 0.314 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 1/2 inch RMC?
At the NEC 40% fill limit for three or more conductors, 1/2 inch RMC (internal area 0.314 sq in) holds 9 #12 THHN, 13 #14, 6 #10, or 3 #8 conductors. The math is the conduit area times 0.40 (0.314 × 0.40 = 0.126 sq in allowable), divided by the conductor's area from NEC Chapter 9 Table 5.
How many 12 AWG THHN wires fit in 1/2 inch RMC?
9 #12 THHN conductors fit in 1/2 inch RMC at the 40% fill limit. Each #12 THHN is 0.0133 sq in, so 0.126 sq in allowable ÷ 0.0133 rounds to 9 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 1/2 inch RMC?
6 #10 THHN conductors fit in 1/2 inch RMC at the NEC 40% fill limit. Each #10 THHN is 0.0211 sq in, so 0.126 sq in allowable (0.314 × 0.40) ÷ 0.0211 rounds to 6 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 1/2 inch RMC?
13 #14 THHN conductors fit in 1/2 inch RMC at 40% fill. Each #14 THHN is 0.0097 sq in, so 0.126 sq in ÷ 0.0097 rounds to 13 (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 1/2 inch RMC?
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 1/2 inch RMC (internal area 0.314 sq in, RMC (rigid metal conduit)) that is 0.166 sq in for one wire, 0.097 sq in for two, and 0.126 sq in for three or more. The 40% case is the common one.
Fill for Other RMC Sizes
Wires in 3/4" RMC
16 #12 THHN and the full count for 3/4 inch pipe.
Wires in 1" RMC
26 #12 THHN and the full count for 1 inch pipe.
Wires in 1-1/4" RMC
46 #12 THHN and the full count for 1-1/4 inch pipe.
Wires in 1-1/2" RMC
62 #12 THHN and the full count for 1-1/2 inch pipe.
Wires in 2" RMC
102 #12 THHN and the full count for 2 inch pipe.
Wires in 2-1/2" RMC
146 #12 THHN and the full count for 2-1/2 inch pipe.
Wires in 3" RMC
225 #12 THHN and the full count for 3 inch pipe.
Wires in 3-1/2" RMC
301 #12 THHN and the full count for 3-1/2 inch pipe.
Wires in 4" RMC
387 #12 THHN and the full count for 4 inch pipe.
1/2" in Other Conduit Types
The same 1/2 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.