Conduit Fill Calculator — Formule
## NEC Conduit Fill Rules
The National Electrical Code limits fill percentages to prevent overheating:
- **1 conductor: 53%**
- **2 conductors: 31%**
- **3 or more: 40%**
Calculate fill by dividing total conductor area (including insulation) by the conduit internal area.
The National Electrical Code limits fill percentages to prevent overheating:
- **1 conductor: 53%**
- **2 conductors: 31%**
- **3 or more: 40%**
Calculate fill by dividing total conductor area (including insulation) by the conduit internal area.
Exemple Résolu
4 conductors of 12 AWG THHN (0.0973 sq in each) in 3/4-inch EMT (0.864 sq in).
- Total wire area = 4 x 0.0973 = 0.389 sq in
- Fill = 0.389 / 0.864 x 100 = 45.0%
- NEC allows 40% for 3+ conductors
- This conduit is overfilled; upsize to 1-inch EMT.