By Blissom · Updated 2026-11-04
1/2" EMT fill by wire type
Chapter 9 Table 4 gives 1/2" EMT an internal area of 0.304 in². With three or more wires you may fill 40% of it. Note 7 lets a result of x.8 or more round up when every wire is the same size.
| Wire | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| #14 | 12 | 8 | 6 |
| #12 | 9 | 6 | 4 |
| #10 | 5 | 5 | 3 |
| #8 | 3 | 2 | 1 |
| #6 | 2 | 1 | 1 |
| #4 | 1 | 1 | 1 |
| #3 | 1 | 1 | 1 |
| #2 | 1 | 1 | 1 |
| #1 | 1 | 1 | 1 |
| #1/0 | 1 | 1 | — |
THW uses the larger Table 5 dimensions that Annex C uses, so it is the cautious count. A single large conductor is allowed 53% fill and two are allowed 31%, which is why one #1/0 still fits.
Fill or derating: which runs out first
The fill count tells you what will physically and legally fit. It says nothing about heat. Bundle more than three current-carrying conductors and each one must be derated.
In 1/2" EMT the pipe is small enough that fill often wins:
- #14 on 15 A: fill allows 12, derating allows 9 current-carrying. Derating is the limit, with room left for neutrals and the ground.
- #12 on 20 A: fill allows 9, derating allows 9 current-carrying. Fill is the limit; one slot goes to the ground.
- #10 on 30 A: fill allows 5, derating allows 6 current-carrying. Fill is the limit; one slot goes to the ground.
Derating bands for #14, #12, #10
THHN is 90 °C wire, so derating starts from the 90 °C column of Table 310.16. The result must still be at least the breaker size, and it may not exceed the 60 °C or 75 °C rating of the terminations (110.14(C)).
| Wire and breaker | Fits by fill | Current-carrying limit | What stops you first |
|---|---|---|---|
| #14 on 15 A | 12 | 9 | Derating |
| #12 on 20 A | 9 | 9 | Fill |
| #10 on 30 A | 5 | 6 | Fill |
The band-by-band derating table (80%, 70%, 50% and lower) is the same for every pipe size; it is on the 3/4" EMT page. The fill count includes one ground, which never counts toward the current-carrying limit.
Read across: #12 holds 21 A at seven to nine wires, enough for a 20 A breaker. At ten it drops to 15 A. #10 on a 30 A breaker is tighter still and stops at 6.
Raceways 24" or shorter skip this adjustment. Hot spaces such as rooftops add an ambient correction under 310.15(B) on top of it.
Counting circuits, neutrals and grounds
Derating counts current-carrying conductors, not wires. The rules that decide what counts:
- Hot conductors always count.
- The neutral of a two-wire circuit carries the full load current, so it counts too. Each 120 V circuit with its own neutral is two.
- A shared neutral on a 120/240 V multiwire circuit carries only the imbalance, so 310.15(E) lets you skip it. Two circuits, two counted.
- Grounds never count for derating (310.15(F)), but they do take up fill.
| Wire and breaker | Two-wire circuits | 120/240 V multiwire |
|---|---|---|
| #14 THHN, 15 A | 4 | 6 |
| #12 THHN, 20 A | 4 | 4 |
| #10 THHN, 30 A | 2 | 2 |
Shared neutrals only pay off with #14 here. With #12, the neutrals eat the same space the extra hots would need. Multiwire circuits also need a handle tie or two-pole breaker so both hots open together (210.4(B)).
Two common 1/2" pulls
Two receptacle circuits and a lighting circuit
Two 20 A, 120 V receptacle circuits on #12 and a 15 A lighting circuit on #14, each with its own neutral, plus one #12 ground.
| Conductors | Area each (in²) | Subtotal (in²) |
|---|---|---|
| 4 × #12 THHN (hots and neutrals, 20 A) | 0.0133 | 0.0532 |
| 2 × #14 THHN (hot and neutral, 15 A) | 0.0097 | 0.0194 |
| 1 × #12 THHN (ground) | 0.0133 | 0.0133 |
| Total, 7 conductors | 0.0859 | |
| Allowed: 40% of 0.304 in² | 0.1216 |
Fill is 28.3%, under the 40% limit. That is 6 current-carrying conductors, factor 80%: #12 drops to 24 A and #14 to 20 A. Both still cover their breakers.
A 240 V, 30 A condenser circuit
Two #10 hots and a #10 ground. No neutral, three conductors, two of them current-carrying.
| Conductors | Area each (in²) | Subtotal (in²) |
|---|---|---|
| 2 × #10 THHN (hots) | 0.0211 | 0.0422 |
| 1 × #10 THHN (ground) | 0.0211 | 0.0211 |
| Total, 3 conductors | 0.0633 | |
| Allowed: 40% of 0.304 in² | 0.1216 |
Fill is 20.8%. No derating applies with only two current-carrying conductors. Adding a 20 A circuit later would bring it to four, factor 80%: #10 keeps 30 A, still enough.
When 1/2" is the wrong pipe
- Pulls near the maximum. 9 #12 is legal, but on a run with several bends it is a hard pull. Insulation damage on a full 1/2" pull is a real risk.
- Long runs with 360° of bends. The 360° limit between pull points is the same for every size. A tight 1/2" run with a full 9 is where a pull point or a 3/4" pipe earns its cost.
- Anything you might add to. A home run that is already at four circuits has no room left. The jump to 3/4" costs little in material and bending effort.
- Mixed sizes. The table above only works when every wire is the same. With a mix, add up the areas or use the conduit fill calculator.
Counts and factors follow NEC 2023. Verify against the edition your inspector enforces.
Sources: NEC 2023: Chapter 9, Tables 1, 4 and 5 with Note 7 (fill); 310.15(C)(1) (adjustment for more than three current-carrying conductors), 310.15(E) and (F) (neutrals and grounds), Table 310.16, 240.4(D) and 110.14(C). Method.
Questions electricians ask
How many wires fit in 1/2 EMT?
9 #12 THHN or 12 #14 THHN, counting the ground. With #10 THHN it is 5, and with #8 THHN it is 3. XHHW and THW are thicker, so fewer fit.
How many 20 amp circuits can I run in 1/2 EMT?
4 two-wire 20 A circuits on #12 THHN plus an insulated #12 ground. Using 120/240 V multiwire circuits with shared neutrals still gives 4, because the extra neutrals use up the remaining fill.
How many 15 amp circuits fit in 1/2 inch EMT?
On #14 THHN, 4 two-wire circuits, or 6 circuits as 120/240 V multiwire branch circuits with handle-tied breakers. Beyond 9 current-carrying #14 conductors the derated ampacity falls below 15 A.
Does the ground wire count in 1/2 EMT fill?
Yes. An insulated equipment grounding conductor counts in fill at its Table 5 area; a bare one at its Table 8 area. It does not count as a current-carrying conductor for derating.
How many wires can go in 1/2 conduit before derating?
Three current-carrying conductors. From the fourth one on, 310.15(C)(1) applies. Derating reduces ampacity; it does not stop you adding wires until the reduced value drops below the breaker size.
Check 1/2" fill before you pull
- NEC conduit fill with mixed wire sizes and grounds
- Box fill for the boxes at each end
- Offsets, saddles and 90s for the same run
- Works offline in a basement or crawlspace
Android only. There is no iPhone version yet; the free calculators on this site work on any phone.
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