Conduit Fill Chart & Calculator
How many wires fit in a conduit, for every common raceway and building wire. Pick a conduit and wire below for an instant answer, or use the charts — every count is calculated from the conduit’s internal area and the wire’s insulated area using the NEC Chapter 9 fill limits.
Quick answer: 1/2-inch EMT holds 9 #12 THHN wires and 3/4-inch EMT holds 16. The limit is 40% fill for three or more conductors, 31% for two and 53% for one.
Conduit fill calculator
Loading calculator…
EMT conduit fill chart — THHN / THWN-2
The most-used combination. Click a trade size for that conduit’s full chart, or a wire size for everything about that gauge.
| Wire 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 | 1 | 4 | 7 | 12 | 16 | 26 | 46 | 69 | 91 | 116 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 16 | 28 | 43 | 56 | 71 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 | 24 | 36 | 47 | 60 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 11 | 20 | 30 | 40 | 51 |
| 1 AWG | 1 | 1 | 1 | 4 | 5 | 8 | 15 | 22 | 29 | 37 |
| 1/0 AWG | — | 1 | 1 | 3 | 4 | 7 | 12 | 19 | 25 | 32 |
| 2/0 AWG | — | 1 | 1 | 2 | 3 | 6 | 10 | 16 | 20 | 26 |
| 3/0 AWG | — | 1 | 1 | 1 | 3 | 5 | 8 | 13 | 17 | 22 |
| 4/0 AWG | — | — | 1 | 1 | 1 | 4 | 7 | 11 | 14 | 18 |
| 250 kcmil | — | — | 1 | 1 | 1 | 3 | 6 | 9 | 11 | 15 |
| 300 kcmil | — | — | — | 1 | 1 | 3 | 5 | 7 | 10 | 13 |
| 350 kcmil | — | — | — | 1 | 1 | 1 | 4 | 6 | 9 | 11 |
| 400 kcmil | — | — | — | 1 | 1 | 1 | 4 | 6 | 8 | 10 |
| 500 kcmil | — | — | — | 1 | 1 | 1 | 3 | 5 | 6 | 8 |
| 600 kcmil | — | — | — | — | 1 | 1 | 2 | 4 | 5 | 7 |
| 700 kcmil | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 6 |
| 750 kcmil | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| 800 kcmil | — | — | — | — | — | 1 | 1 | 3 | 4 | 5 |
| 900 kcmil | — | — | — | — | — | 1 | 1 | 3 | 3 | 4 |
| 1000 kcmil | — | — | — | — | — | 1 | 1 | 2 | 3 | 4 |
Fill charts by conduit type
EMT fill chart
Thin-wall galvanized steel tubing joined with set-screw or compression fittings.
Article 352PVC Schedule 40 fill chart
Gray nonmetallic conduit for underground runs, slabs and wet or corrosive locations.
Article 352PVC Schedule 80 fill chart
Heavy-wall PVC required where conduit is exposed to physical damage, such as risers on poles and service masts.
Article 344Rigid Metal Conduit fill chart
Threaded heavy-wall galvanized steel (or aluminum) conduit.
Article 342IMC fill chart
Threaded steel conduit with a thinner wall than rigid.
Article 348Flexible Metal Conduit fill chart
Spiral-wound interlocked steel or aluminum “Greenfield”.
Article 350Liquidtight Flexible Metal Conduit fill chart
Flexible metal conduit with a sunlight- and oil-resistant thermoplastic jacket.
Article 362ENT fill chart
Corrugated pliable plastic tubing (“smurf tube”), bent by hand and used inside walls, above suspended ceilings and encased in concrete slabs.
NEC conduit fill percentages
| Conductors in the raceway | Maximum fill | Why |
|---|---|---|
| 1 | 53% | A single conductor cannot jam, so more of the area can be used. |
| 2 | 31% | Two conductors lie side by side and wedge easily in bends, so the limit is lowest. |
| 3 or more | 40% | The everyday limit. Leaves room to pull and for heat to escape. |
| Nipple ≤ 24 in. | 60% | Short sections between boxes or enclosures; derating for conductor count does not apply either. |
How to calculate conduit fill
- Find the conduit’s internal area. It depends on the type as well as the trade size — 3/4-inch EMT is 0.533 in² inside, 3/4-inch Schedule 80 PVC only 0.409 in².
- Find each conductor’s area including insulation. A 12 AWG THHN is 0.0133 in²; the same copper with THW insulation is 0.0181 in².
- Add the areas of every conductor: hots, neutrals, grounds and spares.
- Compare with the limit for that number of conductors: 53%, 31% or 40% of the conduit’s area.
max wires = ⌊ conduit area × 0.40 ÷ area of one wire ⌋ (round up at .8 or more)
Worked example. Three 8 AWG THHN and one 10 AWG THHN ground in 1/2-inch EMT: 3 × 0.0366 + 0.0211 = 0.1309 in². The 40% allowance is 0.304 × 0.40 = 0.1216 in². It does not fit — go to 3/4-inch (0.2132 in² allowed).
Fill is not the only limit. Once a raceway holds more than three current-carrying conductors, their ampacity must be reduced — see the derating factors. Nine #12s fit in 1/2-inch EMT, but at a 70% adjustment they are still good for 20 A only because THHN starts from its 90°C rating.
Conduit internal area compared
| Trade size | EMT | PVC Sch. 40 | PVC Sch. 80 | RMC | IMC | FMC | LFMC | ENT |
|---|---|---|---|---|---|---|---|---|
| 1/2" | 0.122 | 0.114 | 0.087 | 0.126 | 0.137 | 0.127 | 0.126 | 0.114 |
| 3/4" | 0.213 | 0.203 | 0.164 | 0.220 | 0.234 | 0.213 | 0.216 | 0.203 |
| 1" | 0.346 | 0.333 | 0.275 | 0.355 | 0.384 | 0.327 | 0.349 | 0.333 |
| 1-1/4" | 0.598 | 0.581 | 0.495 | 0.610 | 0.659 | 0.511 | 0.611 | 0.581 |
| 1-1/2" | 0.814 | 0.794 | 0.684 | 0.828 | 0.890 | 0.743 | 0.792 | 0.794 |
| 2" | 1.342 | 1.316 | 1.150 | 1.363 | 1.452 | 1.308 | 1.298 | 1.316 |
| 2-1/2" | 2.343 | 1.878 | 1.648 | 1.946 | 2.054 | 1.964 | 1.952 | — |
| 3" | 3.538 | 2.907 | 2.577 | 3.000 | 3.169 | 2.828 | 2.990 | — |
| 3-1/2" | 4.618 | 3.895 | 3.475 | 4.004 | 4.234 | 3.848 | 3.892 | — |
| 4" | 5.901 | 5.022 | 4.503 | 5.153 | 5.452 | 5.026 | 5.077 | — |
Frequently asked questions
What is the maximum conduit fill allowed by the NEC?
40% of the conduit's internal cross-sectional area when it holds three or more conductors, 31% for exactly two, and 53% for a single conductor. A nipple 24 inches or shorter may be filled to 60%.
How do you calculate conduit fill?
Add up the cross-sectional area of every conductor, insulation included, and divide by the internal area of the conduit. For same-size wires: multiply the conduit area by 0.40 and divide by the area of one wire. 1/2-inch EMT has 0.304 in² inside; 40% is 0.1216 in²; 12 AWG THHN is 0.0133 in²; 0.1216 ÷ 0.0133 = 9.1, so 9 wires.
How many #12 wires fit in 1/2-inch and 3/4-inch EMT?
9 conductors of 12 AWG THHN fit in 1/2-inch EMT and 16 fit in 3/4-inch EMT. Remember that more than three current-carrying conductors also triggers ampacity derating, which usually becomes the practical limit before fill does.
Do ground wires and neutrals count toward conduit fill?
Yes. Every conductor in the raceway takes up space, so equipment grounding conductors, neutrals and spares all count toward fill, using their actual area (a bare ground uses its bare-conductor area). Grounds are excluded only from the separate count of current-carrying conductors used for ampacity adjustment.
When do I round up the number of conductors?
When all conductors are the same size and the calculation lands at 0.8 or higher past a whole number, the next whole number is allowed. 3/4-inch EMT works out to 21.98 × 14 AWG THHN, which is treated as 22.
How is a multiconductor cable counted?
A cable such as NM or MC pulled into conduit is treated as one conductor. Use its actual outside diameter to work out the area (for an oval cable, use the wider dimension as the diameter), and apply the 53% single-conductor limit if it is alone.
NECTables.com is an independent reference and is not affiliated with, endorsed by, or a substitute for the National Fire Protection Association (NFPA). NEC® and National Electrical Code® are registered trademarks of the NFPA. Values shown are commonly published engineering data and independent calculations based on the methods of NFPA 70; they are not a reproduction of the Code. Always confirm against the edition adopted in your jurisdiction, including local amendments, and consult a licensed electrician or engineer before doing electrical work.