Conduit Capacity Planner
Plan how many conductors of different sizes fit in a conduit with NEC 40% fill limit visualization.
Results
Visualization
How It Works
When running multiple wire sizes in a single conduit, you must add each wire's area individually and compare the total to the NEC fill limit. This planner handles mixed wire sizes that the basic conduit fill calculator cannot.
The Formula
Total Area = (n14 × 0.0097) + (n12 × 0.0133) + (n10 × 0.0211) + (n8 × 0.0366) + (n6 × 0.0507)
Fill % = Total Area / Conduit Area × 100
Fill % = Total Area / Conduit Area × 100
Variables
- n_x — Number of wires of each AWG gauge size
- Wire Area — THHN cross-sectional area for each gauge from NEC Chapter 9 Table 5
- Conduit Area — Internal area of conduit from NEC Chapter 9 Table 4
Example
Three 12 AWG and two 10 AWG in 3/4" EMT: (3 x 0.0133) + (2 x 0.0211) = 0.0399 + 0.0422 = 0.0821 sq in. Conduit = 0.533 sq in. Fill = 15.4%. Well under 40%.
Tips
- This planner uses THHN wire areas, the most common insulation type for raceway wiring.
- For other insulation types, wire areas differ and you should consult NEC Chapter 9 Table 5.
- A doughnut chart shows at a glance how much capacity remains for future additions.
- Plan for at least 25% spare capacity if future circuits may be added.
- When mixing wire types (THHN, XHHW, etc.), use each wire type's specific area.