What is maximum conduit fill?

NEC limits fill to 53% for 1–2 conductors, 31% for 3+, and 40% for over 4 in some cases—this tool applies approximate limits.

Conduit Fill Calculator — NEC Wire Fill

Check electrical conduit fill percentage and max conductors per NEC Chapter 9. Free conduit fill calculator.

Conduit size

Wire size

Number of conductors

Formula used

Fill % = (N × Wire area) ÷ Conduit area
Compare to NEC max fill tables

Examples

Try a sample calculation

3/4 in, three 12 AWG

Typical branch

Fill percent and pass/fail.

Max wire count estimate.

Enter the required fields—dates, amounts, percentages, or measurements as labeled.
Double-check units (currency, tax rate, height/weight) match your scenario.
Run the calculation and read the breakdown, not just the headline number.
Adjust inputs to compare scenarios, or open a related Rankify calculator for the next step.

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