Electrical calculator
Conduit Fill Calculator
Calculate how many wires fit in a conduit per NEC guidelines.
About the conduit fill calculator
The conduit fill calculator determines how many wires fit in a conduit per NEC guidelines.
How to use this calculator
- 1
Choose conduit size
Select the conduit diameter.
- 2
Enter wire gauge
Enter the AWG wire size.
- 3
Choose wire type
Select THHN, Romex, or XHHW.
How the calculation works
NEC allows 40% fill for 3+ wires. Calculates based on wire cross-section area and conduit internal area.
Example: 3/4 inch conduit, 12 AWG THHN: max 16 wires.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about conduit fill calculator
How accurate is the conduit fill calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.