Conduit Fill Chart — Usable Area by Trade Size
Instead of making you multiply percentages mid-pull, this chart leads with the number you actually compare against: the usable wire-fill area in square inches, pre-computed at each NEC fill limit for every trade size of EMT, IMC, RMC, and PVC Schedule 40 and 80. Sum your conductor areas, find the column for your conductor count, and check you're under it. Fill limits per NEC Chapter 9, Table 1; internal areas per Table 4.
EMT — Electrical Metallic Tubing
Thin-wall steel tubing, the workhorse for interior commercial runs. Made in trade sizes 1/2" through 4".
| Trade size | 3+ wires (40%) | 2 wires (31%) | 1 wire (53%) | Nipple ≤24″ (60%) | Internal area (100%) |
|---|---|---|---|---|---|
| 1/2" | 0.122 | 0.094 | 0.161 | 0.182 | 0.304 |
| 3/4" | 0.213 | 0.165 | 0.282 | 0.320 | 0.533 |
| 1" | 0.346 | 0.268 | 0.458 | 0.518 | 0.864 |
| 1-1/4" | 0.598 | 0.464 | 0.793 | 0.898 | 1.496 |
| 1-1/2" | 0.814 | 0.631 | 1.079 | 1.222 | 2.036 |
| 2" | 1.342 | 1.040 | 1.779 | 2.014 | 3.356 |
| 2-1/2" | 2.343 | 1.816 | 3.105 | 3.515 | 5.858 |
| 3" | 3.538 | 2.742 | 4.688 | 5.308 | 8.846 |
| 3-1/2" | 4.618 | 3.579 | 6.119 | 6.927 | 11.545 |
| 4" | 5.901 | 4.573 | 7.819 | 8.852 | 14.753 |
IMC — Intermediate Metal Conduit
Lighter-wall alternative to rigid with the largest internal area of the steel raceways. Made 1/2" through 4".
| Trade size | 3+ wires (40%) | 2 wires (31%) | 1 wire (53%) | Nipple ≤24″ (60%) | Internal area (100%) |
|---|---|---|---|---|---|
| 1/2" | 0.137 | 0.106 | 0.181 | 0.205 | 0.342 |
| 3/4" | 0.234 | 0.182 | 0.311 | 0.352 | 0.586 |
| 1" | 0.384 | 0.297 | 0.508 | 0.575 | 0.959 |
| 1-1/4" | 0.659 | 0.511 | 0.873 | 0.988 | 1.647 |
| 1-1/2" | 0.890 | 0.690 | 1.179 | 1.335 | 2.225 |
| 2" | 1.452 | 1.125 | 1.924 | 2.178 | 3.630 |
| 2-1/2" | 2.054 | 1.592 | 2.722 | 3.081 | 5.135 |
| 3" | 3.169 | 2.456 | 4.199 | 4.753 | 7.922 |
| 3-1/2" | 4.234 | 3.281 | 5.610 | 6.350 | 10.584 |
| 4" | 5.452 | 4.226 | 7.224 | 8.179 | 13.631 |
RMC — Rigid Metal Conduit
Heavy-wall threaded steel for exposed, wet, and mechanical-abuse locations. Made 1/2" through 6".
| Trade size | 3+ wires (40%) | 2 wires (31%) | 1 wire (53%) | Nipple ≤24″ (60%) | Internal area (100%) |
|---|---|---|---|---|---|
| 1/2" | 0.126 | 0.097 | 0.166 | 0.188 | 0.314 |
| 3/4" | 0.220 | 0.170 | 0.291 | 0.329 | 0.549 |
| 1" | 0.355 | 0.275 | 0.470 | 0.532 | 0.887 |
| 1-1/4" | 0.610 | 0.473 | 0.809 | 0.916 | 1.526 |
| 1-1/2" | 0.828 | 0.642 | 1.098 | 1.243 | 2.071 |
| 2" | 1.363 | 1.056 | 1.806 | 2.045 | 3.408 |
| 2-1/2" | 1.946 | 1.508 | 2.579 | 2.920 | 4.866 |
| 3" | 3.000 | 2.325 | 3.974 | 4.499 | 7.499 |
| 3-1/2" | 4.004 | 3.103 | 5.305 | 6.006 | 10.010 |
| 4" | 5.153 | 3.993 | 6.827 | 7.729 | 12.882 |
| 5" | 8.085 | 6.266 | 10.712 | 12.127 | 20.212 |
| 6" | 11.663 | 9.039 | 15.454 | 17.495 | 29.158 |
PVC Schedule 40
Standard-wall rigid PVC for underground and corrosive locations. Made 1/2" through 6".
| Trade size | 3+ wires (40%) | 2 wires (31%) | 1 wire (53%) | Nipple ≤24″ (60%) | Internal area (100%) |
|---|---|---|---|---|---|
| 1/2" | 0.114 | 0.088 | 0.151 | 0.171 | 0.285 |
| 3/4" | 0.203 | 0.157 | 0.269 | 0.305 | 0.508 |
| 1" | 0.333 | 0.258 | 0.441 | 0.499 | 0.832 |
| 1-1/4" | 0.581 | 0.450 | 0.770 | 0.872 | 1.453 |
| 1-1/2" | 0.794 | 0.616 | 1.053 | 1.192 | 1.986 |
| 2" | 1.316 | 1.020 | 1.744 | 1.975 | 3.291 |
| 2-1/2" | 1.878 | 1.455 | 2.488 | 2.817 | 4.695 |
| 3" | 2.907 | 2.253 | 3.852 | 4.361 | 7.268 |
| 3-1/2" | 3.895 | 3.018 | 5.161 | 5.842 | 9.737 |
| 4" | 5.022 | 3.892 | 6.654 | 7.532 | 12.554 |
| 5" | 7.904 | 6.126 | 10.473 | 11.857 | 19.761 |
| 6" | 11.427 | 8.856 | 15.141 | 17.140 | 28.567 |
PVC Schedule 80
Extra-heavy-wall PVC where exposed to damage — the thick wall costs you internal area. Made 1/2" through 6".
| Trade size | 3+ wires (40%) | 2 wires (31%) | 1 wire (53%) | Nipple ≤24″ (60%) | Internal area (100%) |
|---|---|---|---|---|---|
| 1/2" | 0.087 | 0.067 | 0.115 | 0.130 | 0.217 |
| 3/4" | 0.164 | 0.127 | 0.217 | 0.245 | 0.409 |
| 1" | 0.275 | 0.213 | 0.365 | 0.413 | 0.688 |
| 1-1/4" | 0.495 | 0.383 | 0.656 | 0.742 | 1.237 |
| 1-1/2" | 0.684 | 0.530 | 0.907 | 1.027 | 1.711 |
| 2" | 1.150 | 0.891 | 1.523 | 1.724 | 2.874 |
| 2-1/2" | 1.648 | 1.277 | 2.183 | 2.471 | 4.119 |
| 3" | 2.577 | 1.997 | 3.414 | 3.865 | 6.442 |
| 3-1/2" | 3.475 | 2.693 | 4.605 | 5.213 | 8.688 |
| 4" | 4.503 | 3.490 | 5.967 | 6.755 | 11.258 |
| 5" | 7.142 | 5.535 | 9.463 | 10.713 | 17.855 |
| 6" | 10.239 | 7.935 | 13.567 | 15.359 | 25.598 |
How to use this chart
Add up the cross-sectional areas of every conductor going in the raceway — insulated area, not bare copper, and yes, the equipment grounding conductor counts. Then read the column for how many conductors you're pulling: three or more uses the 40% column, exactly two the 31% column, one alone the 53% column, and a nipple of 24 inches or less the 60% column. If your conductor total exceeds the cell, go up a trade size (or over to a fatter raceway type). The conduit fill calculator does the summing and the size recommendation for you.
Notice how much the walls matter: a 2" PVC Schedule 80 run gives you noticeably less room than 2" EMT, because Schedule 80's thick wall eats internal area. If a pull is tight on paper, checking a different raceway type is often cheaper than a size bump.
What fill doesn't cover
Fill is a geometry rule — it exists so conductors can be pulled without damage and heat can escape. Passing fill does not mean the conductors are electrically happy: four or more current-carrying conductors in one raceway trigger the ampacity adjustment factors of NEC 310.15(C)(1), and long pulls with bends have practical pulling-tension limits well below the code maximum. For runs between boxes, check the wire ampacity chart alongside this one, and verify against the code edition your jurisdiction enforces.
Common questions
How full can a conduit be?
For three or more conductors — the everyday case — total conductor cross-section may occupy at most 40% of the conduit’s internal area. One conductor alone may take 53%, exactly two are limited to 31%, and a conduit nipple no longer than 24 inches may be filled to 60% (rules per NEC Chapter 9, Table 1).
Why is the two-wire limit (31%) lower than the one- and three-wire limits?
Two conductors tend to lie side by side and jam against each other and the raceway wall when pulled, so the code gives that geometry the least room. A single conductor can’t jam (53%), and three or more nest into a more stable bundle (40%).
How many 12 AWG THHN wires fit in 3/4-inch EMT?
The 40% fill area of 3/4" EMT is 0.213 in². A 12 AWG THHN conductor occupies 0.0133 in², so 0.213 ÷ 0.0133 = 16 conductors. Remember every wire counts toward fill — including the equipment grounding conductor — and heavy conductor counts trigger ampacity derating long before the conduit is physically full.
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