Conduit Fill Calculator

Calculate conduit fill percentage, total conductor area, allowed fill area, spare conduit capacity, and fill status from wire size, conductor count, insulation type, conduit type, and conduit trade size.

Calculate Conduit Fill

Conduit fill percent = Total conductor area ÷ conduit internal area × 100.
Your result will appear here.

How the conduit fill calculator works

Total conductor area:
The calculator multiplies each conductor area by the number of conductors.

Fill percentage:
The total conductor area is divided by the selected conduit internal area.

Fill status:
The result is compared against the selected fill limit to show whether the conduit is under, near, or over the fill target.

Why use a conduit fill calculator?

A conduit fill calculator helps estimate whether selected wires fit inside a selected conduit size.

It can help with branch circuits, feeder runs, garage wiring, shed wiring, equipment circuits, panel work, low-voltage conduit, and general electrical planning.

What your result means

Your result shows conduit fill percentage, fill status, selected conduit size, recommended conduit size, conductor area, allowed area, spare area, conductor count, and comparison scenarios.

Conduit fill calculator formulas

Frequently asked questions

What is conduit fill?

Conduit fill is the percentage of conduit space occupied by wires or conductors.

What is the common conduit fill limit?

A common planning estimate is 40% fill for more than two conductors, 31% for two conductors, and 53% for one conductor.

Do ground wires count in conduit fill?

Yes. Ground wires take up physical space inside the conduit and should be included in conduit fill estimates.

Can this replace NEC conduit fill tables?

No. This calculator is a simplified planning tool. Always verify conductor type, conduit type, derating, box fill, bend limits, and local code requirements with a qualified electrician.