Conduit Fill Chart: Max THHN Conductors per EMT Size (NEC)
Pull too many wires into a conduit and you'll fight the pull, damage insulation, and cook the conductors — the NEC fill limits exist because jammed wires can't shed heat. This chart gives you the maximum number of THHN/THWN-2 conductors per EMT trade size for the most common gauges, computed from NEC Chapter 9 Tables 1, 4, and 5, plus the fill rules and a worked example you can copy for your next run.
The fill rules (NEC Chapter 9, Table 1)
Conduit fill is measured as the total cross-sectional area of all conductors divided by the internal area of the raceway:
| Number of conductors in the raceway | Maximum fill |
|---|---|
| 1 conductor | 53% |
| 2 conductors | 31% |
| 3 or more conductors | 40% |
| Nipples 24" or less | 60% |
Two conductors get *less* fill than three (31% vs 40%) because two round wires wedge side-by-side and jam — the geometry is worse, not better.
EMT conduit fill chart — THHN/THWN-2 copper (40% fill, 3+ conductors)
Maximum conductor counts per EMT trade size, computed from NEC Chapter 9 Table 4 (EMT areas) and Table 5 (THHN/THWN-2 conductor areas). Always verify against the current code tables for your exact insulation type — compact-strand, XHHW, and TFN have different diameters.
| EMT trade size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG | 1/0 AWG |
|---|---|---|---|---|---|---|---|---|
| 1/2" | 12 | 9 | 5 | 3 | 2 | 1 | 1 | — |
| 3/4" | 21 | 16 | 10 | 5 | 4 | 2 | 1 | 1 |
| 1" | 35 | 26 | 16 | 9 | 6 | 4 | 2 | 1 |
| 1-1/4" | 61 | 44 | 28 | 16 | 11 | 7 | 5 | 3 |
| 1-1/2" | 84 | 61 | 38 | 22 | 15 | 9 | 7 | 4 |
| 2" | 138 | 101 | 63 | 36 | 26 | 16 | 11 | 7 |
Reading the chart: find your wire gauge across the top, read down to the conduit size. A 3/4" EMT legally holds up to 16 × 12 AWG THHN conductors at 40% fill.
The chart is only half the story — derating
Conduit fill tells you what *fits*; NEC 310.15(C)(1) tells you what the wires can *carry* once they're in there. More than three current-carrying conductors in one raceway triggers ampacity adjustment:
| Current-carrying conductors | Ampacity adjustment |
|---|---|
| 4–6 | 80% |
| 7–9 | 70% |
| 10–20 | 50% |
Grounding conductors and (usually) the neutral of a balanced 120/240V circuit don't count as current-carrying. Example: nine 12 AWG THHN conductors in a 3/4" EMT fit fine (limit is 16), but their adjusted ampacity drops from the 90°C base by 70% — often pushing you to upsize wire or split the run into two conduits. This is the single most- missed step in DIY conduit work, and it fails inspections.
How to use this chart
- List every conductor in the run — hots, neutrals that count, and note that the equipment ground counts toward fill but not toward derating.
- Check the count against the 40% column above (or 31%/53% for 2-wire and single-wire runs).
- Apply the ampacity adjustment if you have 4+ current-carrying conductors, and confirm the adjusted ampacity still exceeds the breaker size.
- Size up one trade size for long runs, more than two 90° bends (360° total max between pull points per NEC 358.26), or future expansion — your future self will thank you.
Worked example: garage subpanel feed plus two branch circuits
You're running one EMT from a house panel to a detached garage: a 60A feeder (3 × 6 AWG: two hots + neutral, plus a 10 AWG ground) and you want to add a 20A circuit for yard outlets (2 × 12 AWG).
- Fill check: 3 × 6 AWG + 2 × 12 AWG + 1 × 10 AWG ground. Conductor areas from NEC Table 5: 6 AWG THHN = 0.0507 in², 12 AWG = 0.0133 in², 10 AWG = 0.0211 in². Total = 3(0.0507) + 2(0.0133) + 0.0211 = 0.1998 in².
- 1" EMT at 40% = 0.346 in² → fits with room to spare. 3/4" EMT at 40% = 0.213 in² → also fits, barely (94% of the legal fill) — bad plan for a 100-foot pull with bends.
- Derating check: 5 current-carrying conductors (the feeder neutral counts here) = 80% adjustment. The 6 AWG THHN's 90°C base ampacity is 75A; 75 × 0.80 = 60A — still OK for the 60A breaker, with zero margin.
- Decision: 1" EMT. It pulls easier, keeps the derating legal, and leaves room for a future circuit. Buy an extra stick — nothing hurts like being one conduit short on a Saturday.
EMT vs PVC vs rigid: choosing the raceway
The fill chart above is EMT-specific because EMT is the most common residential/light-commercial raceway — but the right raceway depends on where the run lives:
- EMT ("thinwall"): indoor and covered outdoor runs, garages, basements, commercial interiors. Cheap, fast, bends with a hand bender. Not for direct burial or where subject to severe physical damage.
- PVC Schedule 40/80: direct burial and wet locations — the standard for underground feeders and solar ground runs. Note PVC Schedule 40 has a *smaller* internal area than EMT of the same trade size, so the fill counts above don't transfer — recompute from NEC Chapter 9 Table 4 (Article 352). Expansion fittings are required on long outdoor runs; PVC moves a lot with temperature.
- RMC / IMC (rigid metal): physical protection where conduit is exposed to damage — service masts, drive-under runs, industrial floors. Threads like pipe, costs like pipe.
- LFMC / LFNC (liquidtight flex): short final connections to motors, HVAC condensers, and equipment that vibrates or needs alignment slack.
Two rules that apply everywhere: underground runs need burial depth per NEC Table 300.5 (18" for PVC under residential driveways, 6" for rigid in many cases), and every raceway that enters a building from underground needs sealing against moisture and gas migration. Budget a pull string and a few extra couplings — conduit math on paper always meets physics in the trench.
Frequently asked questions
What percentage can you fill a conduit?
53% for one conductor, 31% for two, 40% for three or more (NEC Chapter 9, Table 1). Short nipples 24 inches or less may go to 60%.
How many 12 AWG wires fit in 1/2 inch EMT?
Nine THHN/THWN-2 conductors at 40% fill. But nine current-carrying conductors would derate to 50% ampacity — in practice, keep 1/2" EMT to one or two circuits.
Does the ground wire count in conduit fill?
Yes — every conductor in the raceway, including equipment grounding conductors, counts toward the cross-sectional fill. Grounds do *not* count as current-carrying conductors for derating.
Is EMT, PVC, or rigid conduit different for fill?
Yes — each raceway type and size has its own internal area in NEC Chapter 9 Table 4. PVC Schedule 40 has a slightly smaller internal area than EMT of the same trade size, so it holds fewer conductors. This chart is EMT-specific.
How many bends can I have in one conduit run?
A maximum of 360° of bends total (for example, four 90s) between pull points. More than that and you need a junction box or conduit body.
Conduit, wire, and fittings — in stock
Portlandia Electric Supply stocks raceway, fittings, and the THHN/THWN-2 to fill them — like Cerro 8 AWG THHN/THWN-2 stranded copper 500' spools and larger feeders like Cerro 1/0 AWG THHN/THWN-2. Browse the Electrical Components collection and Allied Tube & Conduit, and check our wire ampacity chart to confirm your derated conductors still carry the load. Questions on a tricky fill? Call the counter.