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NEC Chapter 9 — Table 4 conduit areas and Table 5 conductor areas
Find the minimum trade size for your conductor count, or the maximum conductors allowed in a conduit you already have. Includes pull-difficulty advisories and jam-ratio warnings from the NEC informational note.
NEC Chapter 9 — Conductor area (sq in, Table 5)
| Wire size | THHN/THWN | XHHW/XHHW-2 | THW/THHW | Fill rule (3+) |
|---|---|---|---|---|
| 14 AWG | 0.0097 | 0.0097 | 0.0139 | 40% |
| 12 AWG | 0.0133 | 0.0133 | 0.0181 | 40% |
| 10 AWG | 0.0211 | 0.0243 | 0.0243 | 40% |
| 8 AWG | 0.0366 | 0.0437 | 0.0437 | 40% |
| 6 AWG | 0.0507 | 0.0590 | 0.0590 | 40% |
| 4 AWG | 0.0824 | 0.0814 | 0.0814 | 40% |
| 3 AWG | 0.0973 | 0.0962 | 0.0962 | 40% |
| 2 AWG | 0.1158 | 0.1146 | 0.1146 | 40% |
| 1 AWG | 0.1562 | 0.1534 | 0.1534 | 40% |
| 1/0 AWG | 0.1855 | 0.1825 | 0.1825 | 40% |
| 2/0 AWG | 0.2223 | 0.2190 | 0.2190 | 40% |
| 3/0 AWG | 0.2660 | 0.2642 | 0.2642 | 40% |
| 4/0 AWG | 0.3237 | 0.3197 | 0.3197 | 40% |
| 250 kcmil | 0.3970 | 0.3904 | 0.3904 | 40% |
| 300 kcmil | 0.4608 | 0.4536 | 0.4536 | 40% |
| 350 kcmil | 0.5242 | 0.5166 | 0.5166 | 40% |
| 400 kcmil | 0.5863 | 0.5782 | 0.5782 | 40% |
| 500 kcmil | 0.7073 | 0.6984 | 0.6984 | 40% |
Conduit internal area — 40% fill column (NEC Table 4)
| Trade size | EMT (40%) | PVC 40 (40%) | PVC 80 (40%) | RMC (40%) | IMC (40%) |
|---|---|---|---|---|---|
| 1/2" | 0.122 in² | 0.114 in² | 0.087 in² | 0.125 in² | 0.137 in² |
| 3/4" | 0.213 in² | 0.203 in² | 0.164 in² | 0.220 in² | 0.235 in² |
| 1" | 0.346 in² | 0.333 in² | 0.275 in² | 0.355 in² | 0.384 in² |
| 1-1/4" | 0.598 in² | 0.581 in² | 0.495 in² | 0.610 in² | 0.659 in² |
| 1-1/2" | 0.814 in² | 0.794 in² | 0.684 in² | 0.829 in² | 0.890 in² |
| 2" | 1.342 in² | 1.316 in² | 1.150 in² | 1.363 in² | 1.452 in² |
| 2-1/2" | 2.343 in² | 1.878 in² | 1.648 in² | 2.181 in² | 2.054 in² |
| 3" | 3.538 in² | 2.907 in² | 2.577 in² | 3.234 in² | 3.169 in² |
| 3-1/2" | 4.618 in² | 3.895 in² | 3.475 in² | 4.232 in² | 4.137 in² |
| 4" | 5.901 in² | 5.022 in² | 4.503 in² | 5.452 in² | 5.341 in² |
Data per NEC Chapter 9 Tables 1, 4, and 5. Always verify with the current NEC edition and local amendments.
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Conduit bending, wire, and pull tools
Field picks for bending EMT, pulling stranded THHN, and tracing circuits after you size the raceway.
Klein Tools 56401 1/2" EMT Conduit Bender
- Built for 1/2" EMT — common residential and light commercial
- Degree markings cast into the head
- Heavy-duty cast iron head
- Size the raceway first, then bend with confidence
Southwire THHN 12 AWG Stranded — 500 ft
- THHN/THWN-2 — matches Table 5 THHN column
- Stranded — easier pulls in calculated fill
- UL listed spool for long homeruns
Greenlee 200 ft Stainless Fish Tape
- Long pulls through conduit and occupied raceways
- Flexible for bends per your fill plan
- Durable steel tape
Electrical Conduit Bending Reference Chart
- Wall chart for offsets, kicks, and saddles
- Covers EMT, IMC, and rigid
- Quick shop or van reference
Klein Tools ET310 Circuit Breaker Finder
- Find the right breaker before de-energizing work
- Transmitter and receiver kit
- Useful after homerun and conduit planning
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How to use this calculator
Conduit fill is a routine NEC Chapter 9 check. This tool applies Table 5 conductor cross-sectional areas and Table 4 total internal raceway areas, then applies Table 1 fill percentages (53% / 31% / 40%, plus 60% for qualifying nipples).
- Mode A — Minimum conduit: Enter conductor count, type, insulation, and size. The smallest listed trade size that satisfies the allowed fill is shown, with actual fill percentage.
- Mode B — Maximum conductors: Pick conduit type and trade size. The tool reports maximum conductors at 40%, 31%, 53%, and 60% (nipple) limits.
- Conduit type: EMT, PVC 40/80, RMC, and IMC have different internal areas at the same trade size — especially PVC Schedule 80.
- Nipple rule: Short nipples (24 in. or less between boxes) may use 60% fill per Table 1, Note 4 — enable the nipple selector when it applies.
Field tip For long runs or several bends, plan below 40% fill when you can. Damaged insulation from a hard pull costs more than upsizing one trade size.
NEC conduit fill and jam ratio
Why fill limits exist
Fill limits support heat dissipation and reduce insulation damage during pulling. The calculator also evaluates the NEC informational jam ratio for three conductors of the same size (ID/OD between 2.8 and 3.2) where geometry can lock conductors even when fill math passes.
Equipment grounding conductors
Every conductor in the raceway counts toward fill, including equipment grounding conductors. (Box fill has different rules for certain grounds — conduit fill does not.)
Mixed wire sizes
With mixed sizes or insulations, sum each conductor’s area from Table 5 and compare to the allowed fill for the raceway. Annex C all-same-size tables do not apply to mixed runs.
Frequently asked questions
What is the maximum conduit fill for three or more wires?
NEC Chapter 9, Table 1 allows 40% of the total internal cross-section for three or more conductors. Two conductors: 31%. One: 53%. Qualifying nipples: 60%.
Does the equipment grounding conductor count?
Yes. All conductors including EGCs count in conduit fill.
Does conduit fill affect ampacity derating?
They are separate rules. More than three current-carrying conductors can trigger 310.15(C)(1) derating even when 40% fill is satisfied.
What is jamming?
With three similar-sized conductors, a conduit ID to conductor OD ratio in the 2.8–3.2 range can physically jam during a pull. The tool warns when that ratio is in range.
Related calculators
Conduit Fill and Heat Dissipation
NEC conduit fill limits — 53% for one conductor, 31% for two, 40% for three or more — are not only about whether wires physically fit. Conductors generate heat under load. Overcrowded conduit traps that heat, reduces effective ampacity over time, and can degrade insulation long before a breaker trips. That is why the NEC pairs fill rules in Chapter 9 with ampacity derating in 310.15(C)(1) when you bundle multiple current-carrying conductors.
Passing a 40% fill calculation does not mean you should always pack to 40% on a hard pull or a long homerun with several bends. Many electricians target lower fill when heat, future expansion, or pull difficulty matters. Upsizing one trade size often costs less than a failed pull, damaged THHN insulation, or a callback for overheating conductors in a crowded raceway.
Audit a Mixed Conductor List
Already know the installed conduit and need to check a mixed list of gauges or insulation types? Use the Wire Fill Calculator, then read the Wire Fill Guide for the 53%/31%/40% rules, mixed-list workflow, grounds, and the difference between raceway fill and box fill.