Conduit Fill Chart — EMT Trade Sizes & Max THHN Conductor Counts (NEC)
EMT conduit fill per NEC Chapter 9: conduit areas from Table 4, THHN/THWN-2 conductor areas from Table 5, and computed max wire counts at 40% fill.
Updated August 20, 2026
Conduit fill is area arithmetic: NEC Chapter 9 Table 4 fixes the internal cross-section of each raceway type, Table 5 fixes the area each insulated conductor occupies, and Table 1 caps how much of the raceway the wires may fill — 53% for one conductor, 31% for two, and 40% for three or more. The first table below carries the EMT (electrical metallic tubing, Article 358) block of Table 4 for trade sizes 1/2″ through 4″: the transcribed nominal inside diameter and total area, with the three percentage columns computed from the total. The second table is the THHN/THWN/THWN-2 column of Table 5, from 14 AWG to 500 kcmil — the same size range as the wire ampacity chart.
The third table divides the two: the maximum number of same-size THHN conductors in each EMT size at 40% fill, applying the Chapter 9 Note (7) rounding rule — the quotient truncates, except a fraction of 0.8 or larger rounds up. Those computed counts reproduce NEC Informative Annex C, Table C.1, which is built by the same arithmetic. The counts apply only when all conductors are the same size; mixed sizes go back to the raw areas (sum the Table 5 areas, compare against the 40% column), which is what the cable tray and conduit sizing calculator automates. Note (4) also caps any single conduit run: equipment grounding conductors count toward fill, and nipples 24″ or shorter may fill to 60%.
EMT Dimensions & Allowable Fill Areas — NEC Ch. 9 Table 4 (Article 358)
| Trade size | Nominal ID (in) | Total area (in²) | 1 wire, 53% (in²) | 2 wires, 31% (in²) | Over 2 wires, 40% (in²) |
|---|---|---|---|---|---|
| 1/2″ | 0.622 | 0.304 | 0.161 | 0.094 | 0.122 |
| 3/4″ | 0.824 | 0.533 | 0.282 | 0.165 | 0.213 |
| 1″ | 1.049 | 0.864 | 0.458 | 0.268 | 0.346 |
| 1-1/4″ | 1.380 | 1.496 | 0.793 | 0.464 | 0.598 |
| 1-1/2″ | 1.610 | 2.036 | 1.079 | 0.631 | 0.814 |
| 2″ | 2.067 | 3.356 | 1.779 | 1.040 | 1.342 |
| 2-1/2″ | 2.731 | 5.858 | 3.105 | 1.816 | 2.343 |
| 3″ | 3.356 | 8.846 | 4.688 | 2.742 | 3.538 |
| 3-1/2″ | 3.834 | 11.545 | 6.119 | 3.579 | 4.618 |
| 4″ | 4.334 | 14.753 | 7.819 | 4.573 | 5.901 |
ID and total area transcribed from Ch. 9 Table 4; the 53/31/40% columns are computed from the total per Ch. 9 Table 1 and Note (4). Nipples ≤ 24″ may fill to 60%.
THHN / THWN / THWN-2 Conductor Dimensions — NEC Ch. 9 Table 5
| Conductor size | Approx. diameter (in) | Approx. area (in²) |
|---|---|---|
| 14 AWG | 0.111 | 0.0097 |
| 12 AWG | 0.130 | 0.0133 |
| 10 AWG | 0.164 | 0.0211 |
| 8 AWG | 0.216 | 0.0366 |
| 6 AWG | 0.254 | 0.0507 |
| 4 AWG | 0.324 | 0.0824 |
| 3 AWG | 0.352 | 0.0973 |
| 2 AWG | 0.384 | 0.1158 |
| 1 AWG | 0.446 | 0.1562 |
| 1/0 AWG | 0.486 | 0.1855 |
| 2/0 AWG | 0.532 | 0.2223 |
| 3/0 AWG | 0.584 | 0.2679 |
| 4/0 AWG | 0.642 | 0.3237 |
| 250 kcmil | 0.711 | 0.3970 |
| 300 kcmil | 0.766 | 0.4608 |
| 350 kcmil | 0.817 | 0.5242 |
| 400 kcmil | 0.864 | 0.5863 |
| 500 kcmil | 0.949 | 0.7073 |
Areas include the insulation, which is why THHN packs tighter than THW or XHHW of the same gauge. THHN, THWN, and THWN-2 share one column in Table 5.
Max Same-Size THHN Conductors per EMT — Computed at 40% Fill
| Conductor size | 1/2″ | 3/4″ | 1″ | 1-1/4″ | 1-1/2″ | 2″ | 2-1/2″ | 3″ | 3-1/2″ | 4″ |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 35 | 61 | 84 | 138 | 241 | 364 | 476 | 608 |
| 12 AWG | 9 | 16 | 26 | 45 | 61 | 101 | 176 | 266 | 347 | 443 |
| 10 AWG | 5 | 10 | 16 | 28 | 38 | 63 | 111 | 167 | 219 | 279 |
| 8 AWG | 3 | 6 | 9 | 16 | 22 | 36 | 64 | 96 | 126 | 161 |
| 6 AWG | 2 | 4 | 7 | 12 | 16 | 26 | 46 | 69 | 91 | 116 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 16 | 28 | 43 | 56 | 71 |
| 3 AWG | 1 | 2 | 3 | 6 | 8 | 13 | 24 | 36 | 47 | 60 |
| 2 AWG | 1 | 2 | 3 | 5 | 7 | 11 | 20 | 30 | 40 | 51 |
| 1 AWG | 0 | 1 | 2 | 4 | 5 | 8 | 15 | 22 | 29 | 37 |
| 1/0 AWG | 0 | 1 | 2 | 3 | 4 | 7 | 12 | 19 | 25 | 32 |
| 2/0 AWG | 0 | 1 | 1 | 2 | 3 | 6 | 10 | 16 | 20 | 26 |
| 3/0 AWG | 0 | 0 | 1 | 2 | 3 | 5 | 8 | 13 | 17 | 22 |
| 4/0 AWG | 0 | 0 | 1 | 2 | 2 | 4 | 7 | 11 | 14 | 18 |
| 250 kcmil | 0 | 0 | 1 | 1 | 2 | 3 | 6 | 9 | 11 | 15 |
| 300 kcmil | 0 | 0 | 0 | 1 | 1 | 3 | 5 | 7 | 10 | 13 |
| 350 kcmil | 0 | 0 | 0 | 1 | 1 | 2 | 4 | 6 | 9 | 11 |
| 400 kcmil | 0 | 0 | 0 | 1 | 1 | 2 | 4 | 6 | 8 | 10 |
| 500 kcmil | 0 | 0 | 0 | 1 | 1 | 2 | 3 | 5 | 6 | 8 |
Computed as (0.40 × Table 4 total area) ÷ Table 5 conductor area with the Ch. 9 Note (7) rounding rule (fraction ≥ 0.8 rounds up) — the same arithmetic that builds Annex C Table C.1. Same-size conductors only; a 0 means that conductor does not fit at 40% fill.
Sources & Further Reading
- NEC (NFPA 70), Chapter 9, Table 4 (Article 358 — EMT) — digit-verified against the buildmyowncabin.com NEC Table 4 reproduction and the conduit.site EMT table (independent reproductions, all ten trade sizes)
- NEC (NFPA 70), Chapter 9, Table 5 (THHN/THWN/THWN-2) — digit-verified against the NEC 2011 Table 5 pages (NECA/IBEW tables reproduction) and the buildmyowncabin.com NEC Table 5 reproduction
- NEC Chapter 9, Table 1 and Notes (4)/(7) — fill percentages and the ≥0.8 rounding rule; computed counts cross-checked against the TSS USA Annex C Table C.1 reproduction
Frequently Asked Questions
How many 12 AWG THHN wires can I pull in 3/4″ EMT?
Sixteen. The 40% fill area of 3/4″ EMT is 0.533 × 0.40 = 0.213 in², and each 12 AWG THHN occupies 0.0133 in², giving 16.03 — which truncates to 16, matching Annex C Table C.1. Remember that equipment grounding conductors count toward fill, and derating under 310.15 usually bites before fill does with that many current-carrying wires.
Why 53% for one wire but only 40% for three or more?
The Chapter 9 Table 1 percentages reflect how conductors pack and pull. A single conductor can safely occupy over half the bore, two conductors sit side by side and are limited to 31% (their pair jams against the wall), and three or more approximate a bundle that needs free space to avoid jamming and insulation damage during the pull — hence 40%. Note (4) adds one exception: conduit nipples up to 24″ may be filled to 60%.
What is the Note (7) 0.8 rounding rule?
When all conductors are the same size, Chapter 9 Note (7) lets a fractional result of 0.8 or more round up to the next whole conductor. That is why 3/4″ EMT takes 22 (not 21) 14 AWG THHN: 0.213 ÷ 0.0097 = 21.98. With mixed sizes there is no rounding allowance — the summed areas simply must not exceed the fill area.
Do these numbers apply to PVC or rigid conduit?
No — each raceway type has its own block in Table 4 because wall thickness differs. Rigid PVC Schedule 80 in particular has a much smaller bore than EMT of the same trade size (1/2″ Sch 80 PVC has a total area of 0.217 in² versus 0.304 in² for EMT), so counts drop. Look up the matching Table 4 block or the corresponding Annex C table for the raceway you are actually running.
Try the Calculators
Conduit Fill Chart — EMT Trade Sizes & Max THHN Conductor Counts (NEC) — reuven.tools/reference/conduit-fill — verified against: NEC (NFPA 70), Chapter 9, Table 4 (Article 358 — EMT) — digit-verified against the buildmyowncabin.com NEC Table 4 reproduction and the conduit.site EMT table (independent reproductions, all ten trade sizes); NEC (NFPA 70), Chapter 9, Table 5 (THHN/THWN/THWN-2) — digit-verified against the NEC 2011 Table 5 pages (NECA/IBEW tables reproduction) and the buildmyowncabin.com NEC Table 5 reproduction; NEC Chapter 9, Table 1 and Notes (4)/(7) — fill percentages and the ≥0.8 rounding rule; computed counts cross-checked against the TSS USA Annex C Table C.1 reproduction