Conduit Fill Calculator
Minimum trade size for EMT, IMC, RMC, PVC Sch 40, and PVC Sch 80, based on the conductors you're pulling. Per NEC Chapter 9 Table 1.
Conductors
Add up to 4 different sizes. Quantity counts every conductor including grounds.
Minimum trade size
—
— % fill
Total conductor area
—
in²
Conduit ID area
—
in²
Fill rule
—
% per NEC Ch. 9
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NEC conduit fill — the three rules
NEC Chapter 9 Table 1 sets the maximum allowable fill percentage of a raceway. It varies by the number of conductors because circular cross-sections nest differently:
- 1 conductor: 53% — no bundling, can use the most space
- 2 conductors: 31% — worst-case jamming geometry, tightest limit
- 3 or more: 40% — bundles average out, this is the typical case
Total conductor area (using Table 5 values for the insulation type) divided by inside area of the conduit (Table 4) must not exceed those percentages.
Fill % = (Σ conductor areas) / (conduit ID area) × 100
What counts as a "conductor"?
Everything you pull through. Phase conductors, neutrals, equipment grounding conductors, isolated grounds, signal pairs — all of them. Pull strings do not count.
When to upsize beyond the minimum
- Long pulls (over ~100 ft) — friction stacks up. Bigger conduit eases the pull.
- Multiple bends (over 360° total) — NEC limits to 360° between pull points; smaller conduit makes that limit binding sooner.
- Wet-location or buried PVC pulls — soap is your friend, more clearance is too.
- Anywhere you might need to add a circuit later.
Quick reference — conductor cross-sections (THHN/THWN-2, NEC Ch. 9 Table 5)
| Size | Area (in²) |
|---|---|
| 14 AWG | 0.0097 |
| 12 AWG | 0.0133 |
| 10 AWG | 0.0211 |
| 8 AWG | 0.0366 |
| 6 AWG | 0.0507 |
| 4 AWG | 0.0824 |
| 3 AWG | 0.0973 |
| 2 AWG | 0.1158 |
| 1 AWG | 0.1562 |
| 1/0 | 0.1855 |
| 2/0 | 0.2223 |
| 3/0 | 0.2679 |
| 4/0 | 0.3237 |
| 250 kcmil | 0.3970 |
| 350 kcmil | 0.5242 |
| 500 kcmil | 0.7073 |
Frequently asked questions
NEC fill limits?
53% for 1 conductor, 31% for 2, 40% for 3+. Total conductor area ÷ conduit ID area.
EMT vs IMC vs RMC?
EMT thin-wall (interior). IMC mid-wall (commercial/outdoor). RMC heavy (hazardous/industrial). RMC has the largest ID, EMT the smallest, for any given trade size.
Do grounds count?
Yes. Every conductor — phases, neutrals, EGCs, IG, signal pairs — all count toward fill.
Spare capacity?
Not required by code, but most contractors upsize one trade size on long runs and anywhere future expansion is likely.