Conduit fill calculator
See how full your conduit is, how many wires fit, and the smallest EMT, PVC, RMC or IMC size for the wires you're pulling.
Your conduit is
17.5% full
WithinOver the 40% limit for 4 wires
- Smallest EMT that fits
- 1/2 in
- Most 12 AWG THHN/THWN-2 alone in 1/2 in
- 9 wires
- Wire area
- 0.0531 sq in
- Conduit inside area
- 0.3039 sq in
- Allowed wire area
- 0.1215 sq in
An estimate from manufacturer dimensions. Inspectors check fill with NEC Chapter 9 Tables 4 and 5, which can differ by a wire. Follow local code and have a licensed electrician lay out the circuits.
How to calculate conduit fill
Add up the cross-section area of every wire, including grounds, and divide by the inside area of the conduit. The National Electrical Code caps how much of that area the wires may take, so they can be pulled without damaging the insulation and don't overheat.
- Wire area = 3.1416 × (wire diameter ÷ 2)², times the number of wires
- Conduit area = 3.1416 × (inside diameter ÷ 2)²
- Fill = total wire area ÷ conduit area
- Limit: 53% for one wire, 31% for two, 40% for three or more
Worked example
Four 12 AWG THHN wires in ½ inch EMT. One wire is about 0.13 in across, so four take 0.0531 sq in. The tubing's inside area is 0.3039 sq in, so the fill is 0.0531 ÷ 0.3039 = 17.5%, well under the 40% limit. Up to 9 of those wires would fit.
Conduit fill chart: THHN wires in EMT
The most THHN/THWN-2 copper wires of one size that fit each trade size of EMT, within the 40% limit (31% for two wires, 53% for one). For RMC, IMC, Schedule 80 or XHHW-2, use the calculator above.
| Wire | ½ in | ¾ in | 1 in | 1¼ in | 1½ in | 2 in | 2½ in | 3 in | 3½ in | 4 in |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 35 | 61 | 84 | 138 | 242 | 365 | 477 | 609 |
| 12 AWG | 9 | 16 | 26 | 45 | 61 | 101 | 176 | 266 | 347 | 444 |
| 10 AWG | 5 | 10 | 16 | 28 | 38 | 63 | 110 | 167 | 218 | 279 |
| 8 AWG | 3 | 5 | 9 | 16 | 22 | 36 | 63 | 96 | 126 | 161 |
| 6 AWG | 1 | 4 | 6 | 11 | 16 | 26 | 46 | 69 | 91 | 116 |
| 4 AWG | 1 | 2 | 4 | 7 | 9 | 16 | 28 | 42 | 56 | 71 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 | 24 | 36 | 47 | 60 |
| 2 AWG | 1 | 1 | 2 | 5 | 7 | 11 | 20 | 30 | 39 | 50 |
| 1 AWG | 1 | 1 | 1 | 3 | 5 | 8 | 14 | 22 | 29 | 37 |
| 1/0 AWG | – | 1 | 1 | 3 | 4 | 7 | 12 | 19 | 24 | 31 |
| 2/0 AWG | – | 1 | 1 | 2 | 3 | 6 | 10 | 15 | 20 | 26 |
| 3/0 AWG | – | 1 | 1 | 1 | 3 | 5 | 8 | 13 | 17 | 22 |
| 4/0 AWG | – | – | 1 | 1 | 1 | 4 | 7 | 10 | 14 | 18 |
| 250 kcmil | – | – | 1 | 1 | 1 | 3 | 5 | 8 | 11 | 14 |
| 300 kcmil | – | – | – | 1 | 1 | 2 | 5 | 7 | 10 | 12 |
| 350 kcmil | – | – | – | 1 | 1 | 1 | 4 | 6 | 8 | 11 |
| 400 kcmil | – | – | – | 1 | 1 | 1 | 3 | 6 | 7 | 10 |
| 500 kcmil | – | – | – | 1 | 1 | 1 | 3 | 5 | 6 | 8 |
PVC conduit fill chart: THHN in Schedule 40
| Wire | ½ in | ¾ in | 1 in | 1¼ in | 1½ in | 2 in | 2½ in | 3 in | 3½ in | 4 in |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 35 | 61 | 84 | 138 | 197 | 305 | 408 | 526 |
| 12 AWG | 9 | 16 | 26 | 45 | 61 | 101 | 144 | 222 | 297 | 383 |
| 10 AWG | 5 | 10 | 16 | 28 | 38 | 63 | 90 | 139 | 187 | 241 |
| 8 AWG | 3 | 5 | 9 | 16 | 22 | 36 | 52 | 80 | 107 | 138 |
| 6 AWG | 1 | 4 | 6 | 11 | 16 | 26 | 37 | 58 | 78 | 100 |
| 4 AWG | 1 | 2 | 4 | 7 | 9 | 16 | 23 | 35 | 47 | 61 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 | 19 | 30 | 40 | 52 |
| 2 AWG | 1 | 1 | 2 | 5 | 7 | 11 | 16 | 25 | 34 | 43 |
| 1 AWG | 1 | 1 | 1 | 3 | 5 | 8 | 12 | 18 | 25 | 32 |
| 1/0 AWG | – | 1 | 1 | 3 | 4 | 7 | 10 | 15 | 21 | 27 |
| 2/0 AWG | – | 1 | 1 | 2 | 3 | 6 | 8 | 13 | 17 | 22 |
| 3/0 AWG | – | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 14 | 19 |
| 4/0 AWG | – | – | 1 | 1 | 1 | 4 | 5 | 9 | 12 | 15 |
| 250 kcmil | – | – | 1 | 1 | 1 | 3 | 4 | 7 | 9 | 12 |
| 300 kcmil | – | – | – | 1 | 1 | 2 | 4 | 6 | 8 | 11 |
| 350 kcmil | – | – | – | 1 | 1 | 1 | 3 | 5 | 7 | 9 |
| 400 kcmil | – | – | – | 1 | 1 | 1 | 3 | 5 | 6 | 8 |
| 500 kcmil | – | – | – | 1 | 1 | 1 | 2 | 4 | 5 | 7 |
Conduit size chart
Inside diameter of each trade size, with the wire area allowed at 40% fill (three or more wires).
| Trade size | EMT | PVC Schedule 40 | PVC Schedule 80 | RMC | IMC |
|---|---|---|---|---|---|
| ½ in | 0.622 in (0.122 sq in) | 0.622 in (0.122 sq in) | 0.546 in (0.094 sq in) | 0.632 in (0.125 sq in) | 0.660 in (0.137 sq in) |
| ¾ in | 0.824 in (0.213 sq in) | 0.824 in (0.213 sq in) | 0.742 in (0.173 sq in) | 0.836 in (0.220 sq in) | 0.864 in (0.235 sq in) |
| 1 in | 1.049 in (0.346 sq in) | 1.049 in (0.346 sq in) | 0.957 in (0.288 sq in) | 1.063 in (0.355 sq in) | 1.105 in (0.384 sq in) |
| 1¼ in | 1.380 in (0.598 sq in) | 1.380 in (0.598 sq in) | 1.278 in (0.513 sq in) | 1.394 in (0.610 sq in) | 1.448 in (0.659 sq in) |
| 1½ in | 1.610 in (0.814 sq in) | 1.610 in (0.814 sq in) | 1.500 in (0.707 sq in) | 1.624 in (0.829 sq in) | 1.683 in (0.890 sq in) |
| 2 in | 2.067 in (1.342 sq in) | 2.067 in (1.342 sq in) | 1.939 in (1.181 sq in) | 2.083 in (1.363 sq in) | 2.150 in (1.452 sq in) |
| 2½ in | 2.731 in (2.343 sq in) | 2.469 in (1.915 sq in) | 2.323 in (1.695 sq in) | 2.489 in (1.946 sq in) | 2.557 in (2.054 sq in) |
| 3 in | 3.356 in (3.538 sq in) | 3.068 in (2.957 sq in) | 2.900 in (2.642 sq in) | 3.090 in (3.000 sq in) | 3.176 in (3.169 sq in) |
| 3½ in | 3.834 in (4.618 sq in) | 3.548 in (3.955 sq in) | 3.364 in (3.555 sq in) | 3.570 in (4.004 sq in) | 3.671 in (4.234 sq in) |
| 4 in | 4.334 in (5.901 sq in) | 4.026 in (5.092 sq in) | 3.826 in (4.599 sq in) | 4.050 in (5.153 sq in) | 4.166 in (5.452 sq in) |
Wire diameters
| Size | THHN/THWN-2 | XHHW-2 |
|---|---|---|
| 14 AWG | 0.111 in (0.0097 sq in) | 0.128 in (0.0129 sq in) |
| 12 AWG | 0.130 in (0.0133 sq in) | 0.146 in (0.0167 sq in) |
| 10 AWG | 0.164 in (0.0211 sq in) | 0.169 in (0.0224 sq in) |
| 8 AWG | 0.216 in (0.0366 sq in) | 0.233 in (0.0426 sq in) |
| 6 AWG | 0.254 in (0.0507 sq in) | 0.272 in (0.0581 sq in) |
| 4 AWG | 0.324 in (0.0824 sq in) | 0.318 in (0.0794 sq in) |
| 3 AWG | 0.352 in (0.0973 sq in) | 0.346 in (0.0940 sq in) |
| 2 AWG | 0.384 in (0.1158 sq in) | 0.377 in (0.1116 sq in) |
| 1 AWG | 0.446 in (0.1562 sq in) | 0.433 in (0.1473 sq in) |
| 1/0 AWG | 0.486 in (0.1855 sq in) | 0.471 in (0.1742 sq in) |
| 2/0 AWG | 0.532 in (0.2223 sq in) | 0.515 in (0.2083 sq in) |
| 3/0 AWG | 0.584 in (0.2679 sq in) | 0.564 in (0.2498 sq in) |
| 4/0 AWG | 0.642 in (0.3237 sq in) | 0.620 in (0.3019 sq in) |
| 250 kcmil | 0.711 in (0.3970 sq in) | 0.685 in (0.3685 sq in) |
| 300 kcmil | 0.766 in (0.4608 sq in) | 0.735 in (0.4243 sq in) |
| 350 kcmil | 0.817 in (0.5242 sq in) | 0.784 in (0.4827 sq in) |
| 400 kcmil | 0.864 in (0.5863 sq in) | 0.831 in (0.5424 sq in) |
| 500 kcmil | 0.949 in (0.7073 sq in) | 0.915 in (0.6576 sq in) |
Sources: inside diameters from Wheatland Tube, Steel EMT Submittal Sheet; JM Eagle, Electrical Conduit Schedule Series Submittal and Data Sheet (rev 9); Wheatland Tube, Rigid Metal Conduit Submittal Sheet; Wheatland Tube, Intermediate Metal Conduit Submittal Sheet; wire diameters from Cerrowire, THHN/THWN-2 data sheet (Rev 02/2026) and Cerrowire, XHHW-2 spec sheet (Rev 05/2026); and fill limits from Service Wire Co., How Do I Calculate Conduit Fill? Manufacturers' dimensions vary slightly, so a chart built on the NEC's own tables can differ by a wire.
Conduit fill questions
How many 12 gauge wires can go in a ½ inch conduit?
9 THHN wires in ½ inch EMT, and 9 in ½ inch Schedule 40 PVC. In ¾ inch EMT, 16 fit. Count the ground wire too. The number that fit isn't the number you can run as current-carrying wires without derating; see the wire size calculator.
How many wires can go in a ¾ inch conduit?
In ¾ inch EMT: 22 THHN wires of 14 AWG, 16 of 12 AWG, 10 of 10 AWG or 5 of 8 AWG. The chart above has every size up to 500 kcmil.
What size conduit do I need for 6/3 wire?
"6/3" usually means a cable with three 6 AWG wires plus a ground. Pulled as separate THHN wires, three 6 AWG and a 10 AWG ground need 3/4 inch EMT or 3/4 inch Schedule 40 PVC. Your ground size depends on the breaker, so enter your own wires above. A whole cable counts as one round conductor at its overall diameter, which you'd get from the cable maker.
What is the 40% conduit fill rule?
With three or more wires, they may take up no more than 40% of the conduit's inside area. One wire may take 53% and two wires 31%, because two round wires side by side can jam in a bend. The rest of the space lets the wires be pulled without scraping the insulation and lets heat escape.
Do ground wires count toward conduit fill?
Yes. Count every wire in the conduit, including grounds and neutrals, and enter bare or green ground wires at their size. Ground wires don't count toward the number of current-carrying wires for derating, but they do take up space.
Why is this different from the NEC or Southwire chart?
This calculator uses manufacturers' published dimensions; inspectors use the National Electrical Code's Chapter 9 tables, and wire brands differ slightly (compact-stranded wire is thinner in large sizes). Charts built on the NEC also round up to the next whole wire when the count comes out at 0.8 or more of one; this calculator counts only whole wires that fit, so it can show one fewer. When you're close to the limit, go up a size or check with the NEC tables.