EMT conduit dimensions
Trade size is a name, not a measurement. Half-inch EMT has an internal diameter of 0.622 inch, not 0.5. The internal area is what the fill calculation uses.
| Trade size | Internal dia (in) | Total area (in²) | 40% fill (in²) | 53% fill (in²) |
|---|---|---|---|---|
| 1/2 | 0.622 | 0.304 | 0.122 | 0.161 |
| 3/4 | 0.824 | 0.533 | 0.213 | 0.283 |
| 1 | 1.049 | 0.864 | 0.346 | 0.458 |
| 1 1/4 | 1.380 | 1.496 | 0.598 | 0.793 |
| 1 1/2 | 1.610 | 2.036 | 0.814 | 1.079 |
| 2 | 2.067 | 3.356 | 1.342 | 1.778 |
| 2 1/2 | 2.731 | 5.858 | 2.343 | 3.105 |
| 3 | 3.356 | 8.846 | 3.538 | 4.688 |
Maximum conductors in EMT
This is the table most jobs actually need. It assumes THHN or THWN insulation and three or more current-carrying conductors, so the 40 percent rule applies.
Remember that filling a conduit to the limit is not the same as a legal circuit. Once you have more than three current-carrying conductors in the same raceway, NEC 310.15(C)(1) derates their ampacity, and the derate can force a larger conductor before fill ever becomes the constraint.
| EMT size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG |
|---|---|---|---|---|---|
| 1/2 | 12 | 9 | 5 | 3 | 2 |
| 3/4 | 22 | 16 | 10 | 6 | 4 |
| 1 | 35 | 26 | 16 | 9 | 7 |
| 1 1/4 | 61 | 45 | 28 | 16 | 12 |
| 1 1/2 | 84 | 61 | 38 | 22 | 16 |
| 2 | 138 | 101 | 63 | 36 | 26 |
The fill percentages and how to calculate
NEC Chapter 9 Table 1 sets three limits: one conductor may occupy 53 percent of the internal area, two conductors 31 percent, and three or more 40 percent. The 31 percent figure for two is lower than for three because two round conductors jam rather than nest.
To work a mixed run by hand, add the individual conductor areas from Chapter 9 Table 5 and compare the total against the 40 percent column above. THHN areas are 0.0097 in² for 14 AWG, 0.0133 for 12, 0.0211 for 10, 0.0366 for 8 and 0.0507 for 6.
Bends matter separately. No run may contain more than 360 degrees of bend between pull points, however much room is left in the conduit.
