Conduit Fill Calculator
Approximate fill % for EMT using Chapter 9–style areas. Not a substitute for the NEC. Click any i for detail.
Conduit and wire
EMT trade size
i
Trade size
Approximate internal area from common EMT sizes. |
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|---|---|
Conductor AWG
i
AWG
THHN/THWN-2 style approximate areas. |
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Conductor count
i
Count
Current-carrying conductors in the raceway (educational). |
How to use this calculator
- Pick EMT trade size.
- Pick AWG.
- Enter how many conductors.
- Compare fill % to the 53/31/40% allowance sketch.
Results explained
NEC Chapter 9 uses 53% (1 wire), 31% (2), and 40% (3+) of conduit internal area. This page uses midpoint areas, not your exact insulation type.
Quick reference: fill allowances
Educational Chapter 9 style.
| Item | Detail |
|---|---|
| 1 conductor | 53% of internal area |
| 2 conductors | 31% |
| 3 or more | 40% |
| Jamming / derating | Separate issues — not modeled |
Always check the actual NEC tables for your insulation and conduit type.
How the estimate is built
used = wire area × count. fill % = used ÷ conduit area. allowed = conduit area × 53/31/40%.
Example scenario
Four #12 THHN-ish in 3/4″ EMT: used ≈ 0.053 in² vs ~0.533 in² conduit → about 10% fill (under 40%).
FAQ
Is this code-legal?
No stamp. It’s a learning sketch. Use NEC tables and local amendments.
What about PVC or IMC?
Internal areas differ. This EMT list will not match.
Ground wires?
EGC counting rules are specific. Don’t assume this count logic covers them.