THHN Wire Fill Chart
THHN maximum conductors across every common conduit type — EMT, IMC, RMC, PVC Sch 40, PVC Sch 80, FMC, LFNC, and ENT — NEC 2023.
THHN is the most-pulled conductor insulation in the US. This wire fill chart switches between every conduit type at a single click so you can pick the right raceway. For mixed-gauge runs, switch to the conduit fill calculator.
| TRADE → WIRE ↓ | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 21 | 35 | 61 | 83 | 138 | 241 | 364 | 476 | 608 |
| 12 AWG | 9 | 16 | 25 | 44 | 61 | 100 | 176 | 266 | 347 | 443 |
| 10 AWG | 5 | 10 | 16 | 28 | 38 | 63 | 111 | 167 | 218 | 279 |
| 8 AWG | 3 | 5 | 9 | 16 | 22 | 36 | 64 | 96 | 126 | 161 |
| 6 AWG | 1 | 4 | 6 | 11 | 16 | 26 | 46 | 69 | 91 | 116 |
| 4 AWG | 1 | 2 | 4 | 7 | 9 | 16 | 28 | 42 | 56 | 71 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 | 24 | 36 | 47 | 60 |
| 2 AWG | 1 | 1 | 2 | 5 | 7 | 11 | 20 | 30 | 39 | 50 |
| 1 AWG | 1 | 1 | 1 | 3 | 5 | 8 | 15 | 22 | 29 | 37 |
| 1/0 | — | 1 | 1 | 3 | 4 | 7 | 12 | 19 | 24 | 31 |
| 2/0 | — | 1 | 1 | 2 | 3 | 6 | 10 | 15 | 20 | 26 |
| 3/0 | — | 1 | 1 | 1 | 3 | 5 | 8 | 13 | 17 | 22 |
| 4/0 | — | — | 1 | 1 | 1 | 4 | 7 | 10 | 14 | 18 |
| 250 | — | — | 1 | 1 | 1 | 3 | 5 | 8 | 11 | 14 |
| 300 | — | — | — | 1 | 1 | 2 | 5 | 7 | 10 | 12 |
| 350 | — | — | — | 1 | 1 | 1 | 4 | 6 | 8 | 11 |
| 400 | — | — | — | 1 | 1 | 1 | 3 | 6 | 7 | 10 |
| 500 | — | — | — | 1 | 1 | 1 | 3 | 5 | 6 | 8 |
| 600 | — | — | — | — | 1 | 1 | 2 | 4 | 5 | 6 |
| 700 | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| 750 | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| 800 | — | — | — | — | — | 1 | 1 | 3 | 4 | 5 |
| 900 | — | — | — | — | — | 1 | 1 | 2 | 3 | 4 |
| 1000 | — | — | — | — | — | 1 | 1 | 2 | 3 | 4 |
EMT — Electrical Metallic Tubing × THHN (90°C dry) · NEC 2023 Ch.9 Tables 4 & 5 · 40% (3+), 31% (2), 53% (1)
NOTES & CONTEXT
What is THHN?
THHN stands for Thermoplastic High Heat-resistant Nylon-coated. Rated 90°C in dry locations, it's the workhorse of US commercial wiring. The dual-rated THWN-2 carries the same Table-5 dimensions as THHN but adds a 90°C wet rating — that's why most modern building wire is stamped THHN/THWN-2 on the same conductor.
THHN wire fill chart math
A 12 AWG THHN conductor occupies 0.0133 in² (Table 5). At NEC's 40% fill, a 1/2" EMT's 0.304 in² interior allows 0.304 × 0.40 = 0.1216 in² of conductor area — so 0.1216 ÷ 0.0133 = 9 conductors. That's the number you'll see in the chart above.
THHN vs RHH conductor area — why insulation matters
The same #12 copper conductor in RHH insulation is 0.0260 in² — almost double THHN's. That's why the chart shows fewer conductors for RHH at the same conduit size. Always confirm the insulation marking before sizing the conduit.
THHN in wet locations
Single-stamped THHN (not THWN-2) is dry-only. If your conduit ever sees moisture — outdoor PVC, underground feeds, even condensation in unconditioned attics — you need THWN-2 or XHHW-2. The fill chart values are the same, so this is purely a code-compliance choice, not a sizing one.