NEC Chapter 9 Conduit Fill
What Size Conduit for Your Wire?
You know the wire; find the pipe. The minimum conduit size for common pulls in EMT, PVC, RMC, and IMC, computed from the NEC Chapter 9 fill limits, with the area math for each.
Minimum Conduit for Common Wire (THHN, 40% Fill)
| Wire | EMT | PVC | RMC | IMC |
|---|---|---|---|---|
| 6/3 | 3/4" | 3/4" | 3/4" | 3/4" |
| 6/2 | 3/4" | 3/4" | 1/2" | 1/2" |
| 8/3 | 3/4" | 3/4" | 3/4" | 1/2" |
| 8/2 | 1/2" | 1/2" | 1/2" | 1/2" |
| 10/3 | 1/2" | 1/2" | 1/2" | 1/2" |
| 10/2 | 1/2" | 1/2" | 1/2" | 1/2" |
| 12/3 | 1/2" | 1/2" | 1/2" | 1/2" |
| 12/2 | 1/2" | 1/2" | 1/2" | 1/2" |
Each pull is figured as individual THHN conductors including the equipment ground. Click a wire for the conductor breakdown, the area math, and the calculator.
Pick Your Wire
Conduit for 6/3 Wire
3/4″ EMT for three #6 plus one #10 ground (0.1732 sq in).
Conduit for 6/2 Wire
3/4″ EMT for two #6 plus one #10 ground (0.1225 sq in).
Conduit for 8/3 Wire
3/4″ EMT for three #8 plus one #10 ground (0.1309 sq in).
Conduit for 8/2 Wire
1/2″ EMT for two #8 plus one #10 ground (0.0943 sq in).
Conduit for 10/3 Wire
1/2″ EMT for three #10 plus one #10 ground (0.0844 sq in).
Conduit for 10/2 Wire
1/2″ EMT for two #10 plus one #10 ground (0.0633 sq in).
Conduit for 12/3 Wire
1/2″ EMT for three #12 plus one #12 ground (0.0532 sq in).
Conduit for 12/2 Wire
1/2″ EMT for two #12 plus one #12 ground (0.0399 sq in).
Conduit Fill Calculator
Any mix of conductors, insulation types, and conduit, with the fill percentage.
Frequently Asked Questions
How do I find what size conduit I need for my wire?
Add the cross-sectional area of every conductor from NEC Chapter 9 Table 5 (including the ground), then divide by the fill limit: 40% for three or more conductors, 31% for two, 53% for one. The result is the minimum internal area, and you pick the smallest conduit trade size at or above it from NEC Chapter 9 Table 4. For example, 10/3 as individual THHN is four #10 conductors and fits 3/4 inch EMT.
Does the ground count when sizing conduit?
Yes. Every conductor in the raceway counts for fill per NEC Chapter 9 Table 1, including the equipment grounding conductor. Forgetting the ground is the most common reason a pull comes out one conduit size too small.