Conduit Fill Calculator (NEC Chapter 9, EMT and PVC)
Conduit fill for THHN/THWN-2 wires in EMT or Schedule 40 PVC: total wire area, percent fill against the NEC 53/31/40% limits, whether it fits, the smallest conduit that does, and the maximum number of same-size wires.
Formula
Wire area = Σ count × Table 5 area (14 AWG 0.0097, 12 AWG 0.0133, 10 AWG 0.0211, 8 AWG 0.0366, 6 AWG 0.0507 sq in …). Allowed = Table 4 conduit area × 53% (1 wire), 31% (2) or 40% (3+). Same-size maximum = allowed ÷ wire area, rounded up only at 0.8 or more.
Worked example
Inputs: Conduit type = EMT (electrical metallic tubing); Trade size = 3/4 in; 14 AWG THHN wires = 6; 12 AWG THHN wires = 0; 10 AWG THHN wires = 0; 8 AWG THHN wires = 0; 6 AWG THHN wires = 0; 4 AWG THHN wires = 0; 3 AWG THHN wires = 0; 2 AWG THHN wires = 0; 1 AWG THHN wires = 0; 1/0 AWG THHN wires = 0.
| Conductors | 6 |
|---|---|
| Conductor area sqin | 0.058 |
| Allowed fill pct | 40 |
| Allowed area sqin | 0.213 |
| Fill pct of conduit | 10.9 |
| Fits | Yes |
| Smallest size that fits | 1/2 in |
| Max same size conductors this conduit | 22 |
NEC Chapter 9: Table 1 allows 53% of the area for 1 conductor, 31% for 2 and 40% for 3 or more; areas from Table 4 (EMT, rigid PVC Schedule 40) and Table 5 (THHN/THWN/THWN-2). Count every insulated conductor, including insulated grounds. Same-size counts round up at 0.8 or more (Note 7). Nipples 24 in or shorter may be filled to 60%. Ampacity adjustment for more than 3 current-carrying conductors is separate.
FAQ
How many 12 gauge wires fit in 1/2 inch EMT?
9 THHN. 1/2 in EMT has 0.304 sq in; 40% is 0.122, and 0.122 ÷ 0.0133 = 9.17, so 9. In 3/4 in EMT it is 16, in 1 in EMT 26.
How many 14 or 10 gauge wires in 1/2 inch EMT?
12 THHN #14 (0.122 ÷ 0.0097 = 12.6) and 5 THHN #10 (5.78). 3/4 in EMT holds 22 #14 or 10 #10.
What is the 40% rule?
NEC Chapter 9 Table 1: one conductor may fill 53% of the conduit, two conductors 31% and three or more 40%. Short nipples (24 in or less) between boxes may be filled to 60%.
Is PVC different from EMT?
Yes, Schedule 40 PVC has a smaller inside area: 1/2 in is 0.285 sq in vs 0.304 for EMT, so it holds 8 #12 THHN instead of 9.
Do ground wires count?
Insulated grounds count like any other conductor. Bare grounds use Table 8 areas, which this calculator does not include. Conduit fill is separate from ampacity adjustment for more than three current-carrying conductors.
Sources
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Last reviewed 2026-10-30.