12 AWG THHN conduit fill chart
These counts use NEC 2023 Chapter 9 Table 4’s published 40% EMT allowances and Table 5’s 0.0133 in² area for one conventional, noncompact 12 AWG THHN/THWN-2 conductor. They apply to standard runs longer than 24 inches with more than two conductors, all the same size and insulation.
The count includes every wire occupying space: line conductors, neutrals, and insulated equipment grounds of that same size. It is not a count of circuits or a promise that every conductor can carry 20 A.
| EMT trade size | 40% allowed area (in²) | Maximum wire count |
|---|---|---|
| ½ in. EMT | 0.122 | 9 |
| ¾ in. EMT | 0.213 | 16 |
| 1 in. EMT | 0.346 | 26 |
How the count is calculated
For ¾-inch EMT, divide the published 0.213 in² allowance by 0.0133 in² per wire: 0.213 ÷ 0.0133 ≈ 16.02. Sixteen wires fit; seventeen occupy 0.2261 in² and exceed the allowance.
Chapter 9 Table 1 Note 7 permits rounding up when a same-size capacity has a fractional part of at least 0.8. None of the three counts above needs that exception. Do not apply this same-size chart or rounding allowance to a mixture of wire sizes.
Does an insulated ground count toward conduit fill?
Yes. If all wires are 12 AWG THHN/THWN-2, an insulated 12 AWG equipment ground uses one of the available spaces. It does not count as a current-carrying conductor for ampacity adjustment.
A differently sized insulated ground changes the total area, so enter it as its own group in the checker. Bare grounds use different dimensions and are outside PassPull’s current catalog. This chart does not select the required equipment-ground size.
Example: three 20 A circuits in ½-inch EMT
For three independent two-wire circuits, take six current-carrying 12 AWG copper conductors plus one insulated 12 AWG equipment ground. Seven wires occupy 0.0931 in²: 30.6% of the conduit’s 0.304 in² total area, below the published 0.122 in² allowance.
At 30°C ambient with verified 75°C terminations, the ampacity calculation is min(30 A × 80%, 25 A) = 24 A. Ordinary 12 AWG copper protection is capped separately at 20 A. A 20 A noncontinuous requirement passes the implemented checks under these assumptions.
Continuous loads, hotter ambient conditions, equipment ratings, circuit grouping, and grounding or bonding requirements still need their applicable checks. This example is not a complete circuit design.
Why fitting in ¾-inch EMT may still fail a 20 A check
Now take five independent two-wire circuits: ten current-carrying 12 AWG copper conductors plus one insulated 12 AWG equipment ground in ¾-inch EMT. The eleven wires occupy 0.1463 in², or 27.4% fill, within the 0.213 in² allowance.
Ten current-carrying conductors use a 50% adjustment factor. At 30°C ambient and verified 75°C terminals, min(30 A × 50%, 25 A) = 15 A. The wires fit, but they do not meet the example’s 20 A noncontinuous requirement.
Increasing conduit size alone does not change that conductor-count factor. Review suitable larger conductors or a different complete-circuit raceway arrangement, then check fill and ampacity together again.
Sources and scope
NEC 2023 Chapter 9 Tables 1, 4, and 5; Table 310.16; Table 310.15(C)(1); 310.15(E) and (F); 110.14(C); and 240.4(D). Calculations use PassPull’s supported catalog, compared with NEC 2023 on September 26, 2026. These examples are also checked against the calculator in automated tests.
This page does not cover nipples 24 inches or shorter, cables, other insulation types, bare grounds, compact conductors, pulling tension, or jam ratio. Verify the adopted code edition, local amendments, actual wire markings, and equipment ratings with a qualified professional.