Conduit Fill Calculator
Calculate conduit fill percentage per NEC code.
Enter conduit size, wire gauge, and number of wires to check if your installation meets electrical code requirements.
Conduit Fill Results
Conduit fill is the percentage of a conduit"s internal area occupied by wires. The National Electrical Code (NEC) limits fill to prevent overheating.
NEC Fill Limits (Chapter 9, Table 1):
- 1 wire: 53% max fill
- 2 wires: 31% max fill
- 3+ wires: 40% max fill
Formula:
Fill % = (Number of Wires x Wire Area) / Conduit Internal Area x 100
Common EMT conduit internal areas:
- 1/2" EMT: 0.304 sq in
- 3/4" EMT: 0.533 sq in
- 1" EMT: 0.864 sq in
- 1-1/4" EMT: 1.496 sq in
- 1-1/2" EMT: 2.036 sq in
- 2" EMT: 3.356 sq in
Common THHN/THWN wire areas (with insulation):
- 14 AWG: 0.0097 sq in
- 12 AWG: 0.0133 sq in
- 10 AWG: 0.0211 sq in
- 8 AWG: 0.0366 sq in
- 6 AWG: 0.0507 sq in
- 4 AWG: 0.0824 sq in
- 2 AWG: 0.1158 sq in
Note: Always verify with the most current NEC edition and local amendments.