Conduit Fill Calculator

Check whether the wires you plan to run fit within the code fill limit for a conduit.

Conduit Fill
— % full
Versus NEC limit.

Usage Tip

Count every conductor including the ground and neutral; derating may also apply when many current-carrying wires share a conduit.

THE MATH
total wire area = wire count × single wire area
fill % = total wire area ÷ conduit area × 100
Code limits how much of a conduit cross-section the wires can fill so they pull through and stay cool. The limit is 53 percent for one wire, 31 percent for two, and 40 percent for three or more.
Pick the conduit size and wire size (areas are listed), and enter the number of wires.
Green means the fill is within the code limit; red means it is over.
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.