Conduit Fill Calculator
Fill percentage against the 53 / 31 / 40 rule, the maximum conductor count for the raceway you picked, and the smallest trade size that legally holds your pull.
Quick answer
Raceway and conductors
A = π × (d / 2)² · fill% = (n × Awire) / Aconduit
12 AWG THHN nominal OD 0.130" = 0.0133 sq in each.
Result
Fill
17.5%
Allowed (3+ wires)
40%
Conduit area
0.3039sq in
Max conductors this size
9
4 conductors are within the 40% limit for 1/2" EMT.
Smallest EMT that holds 4 × 12 AWG THHN: 1/2"
Conductor area used: 0.0531 sq in of 0.1216 sq in permitted.
Maximum THHN conductors per EMT trade size
| Wire size | 1" | 2" | 3" | 4" | 1/2" | 3/4" | 1-1/4" | 1-1/2" | 2-1/2" | 3-1/2" |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 35 | 138 | 365 | 400 | 12 | 22 | 61 | 84 | 242 | 400 |
| 12 AWG | 26 | 101 | 266 | 400 | 9 | 16 | 45 | 61 | 176 | 347 |
| 10 AWG | 16 | 63 | 167 | 279 | 5 | 10 | 28 | 38 | 110 | 218 |
| 8 AWG | 9 | 36 | 96 | 161 | 3 | 5 | 16 | 22 | 63 | 126 |
| 6 AWG | 6 | 26 | 69 | 116 | 1 | 4 | 11 | 16 | 46 | 91 |
| 4 AWG | 4 | 16 | 42 | 71 | 1 | 2 | 7 | 9 | 28 | 56 |
| 3 AWG | 3 | 13 | 36 | 60 | 1 | 1 | 6 | 8 | 24 | 47 |
| 2 AWG | 2 | 11 | 30 | 50 | 1 | 1 | 5 | 7 | 20 | 39 |
| 1 AWG | 1 | 8 | 22 | 37 | 1 | 1 | 3 | 5 | 14 | 29 |
| 1/0 AWG | 1 | 7 | 19 | 31 | — | 1 | 3 | 4 | 12 | 24 |
| 2/0 AWG | 1 | 6 | 15 | 26 | — | 1 | 2 | 3 | 10 | 20 |
| 3/0 AWG | 1 | 5 | 13 | 22 | — | 1 | 1 | 3 | 8 | 17 |
| 4/0 AWG | 1 | 4 | 10 | 18 | — | — | 1 | 1 | 7 | 14 |
Source & method: Raceway internal diameters from UL 797 / ANSI C80.3 nominal dimensions. Conductor areas from manufacturer nominal THHN/THWN-2 outside diameters. Both converted with A = π × (d / 2)².
Internal area by trade size
| Trade size | Internal dia. (in) | Total area (sq in) | 53% (1 wire) | 31% (2 wires) | 40% (3+ wires) |
|---|---|---|---|---|---|
| 1" | 1.049 | 0.8643 | 0.4581 | 0.2679 | 0.3457 |
| 2" | 2.067 | 3.3556 | 1.7785 | 1.0402 | 1.3422 |
| 3" | 3.356 | 8.8457 | 4.6882 | 2.7422 | 3.5383 |
| 4" | 4.334 | 14.7526 | 7.8189 | 4.5733 | 5.9010 |
| 1/2" | 0.622 | 0.3039 | 0.1611 | 0.0942 | 0.1216 |
| 3/4" | 0.824 | 0.5333 | 0.2826 | 0.1653 | 0.2133 |
| 1-1/4" | 1.380 | 1.4957 | 0.7927 | 0.4637 | 0.5983 |
| 1-1/2" | 1.610 | 2.0358 | 1.0790 | 0.6311 | 0.8143 |
| 2-1/2" | 2.731 | 5.8578 | 3.1046 | 1.8159 | 2.3431 |
| 3-1/2" | 3.834 | 11.5450 | 6.1189 | 3.5789 | 4.6180 |
Frequently asked
- What is the maximum conduit fill percentage?
- One conductor may fill 53% of the raceway's internal area, two conductors 31%, and three or more conductors 40%. Short nipples of 24 inches or less are permitted 60% fill.
- How is conduit fill calculated?
- Compute the internal area of the conduit as A = pi x (id/2)^2, compute the area of each conductor from its insulated outside diameter the same way, multiply by the conductor count, then divide the total conductor area by the conduit area.
- How many 12 AWG THHN wires fit in 1/2 inch EMT?
- Half-inch EMT has about 0.304 square inches of internal area. At 40% fill that allows 0.122 square inches. A 12 AWG THHN conductor is about 0.0133 square inches, so nine conductors fit.
- Do I count the ground wire in conduit fill?
- Yes. All conductors occupy space, so the equipment grounding conductor counts toward the fill area even though it is not counted as a current-carrying conductor for ampacity derating.
- Does conduit fill change with conductor type?
- Yes, because fill is based on the insulated outside diameter. THHN/THWN-2 is compact; XHHW and older THW insulation are larger, so fewer conductors fit in the same raceway.
Raceway and pulling supplies
Raceway and pulling supplies
Fittings and lube for the run you just sized.
- 3/4 in EMT conduit3/4 in EMTRaceway in the trade size this fill calculation used.Check price on Amazon →
- 3/4 in connectors & couplings3/4 inFittings sized to match the raceway run.Check price on Amazon →
- Wire pulling lubricantCuts pulling tension on long or high-fill runs.Check price on Amazon →
- Conduit bender3/4 inHand bender matched to this trade size.Check price on Amazon →
Links go to Amazon search results, not a single listing — confirm ratings, insulation type and listing details before buying, and make sure the part is approved for your application.
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