Conduit Fill Calculator

Calculate conduit fill percentage per NEC Chapter 9 rules. Enter your conductor count, wire gauge, and insulation type to find the smallest compliant conduit size and compare costs across EMT, PVC, and Rigid conduit.

Wire Gauge

Insulation Type

Conduit Type

Number of Conductors

Conduit Run Length (ft)

Pricing per 10-ft Stick (edit to match local rates)

1/2" ($/stick)

3/4" ($/stick)

1" ($/stick)

1-1/4" ($/stick)

1-1/2" ($/stick)

2" ($/stick)

Total Wire Area

0.0399 sq in

3 x 12 AWG THHN

NEC Fill Limit

40%

3 conductors

Smallest Compliant

1/2"

$40.00

Conduit Size	Fill Percentage	Cost
1/2" EMTBest value	13.1% fill (OK)	$40.00
3/4" EMT	7.5% fill (OK)	$60.00
1" EMT	4.6% fill (OK)	$100.00
1-1/4" EMT	2.7% fill (OK)	$160.00
1-1/2" EMT	2.0% fill (OK)	$200.00
2" EMT	1.2% fill (OK)	$280.00

Use 1/2" EMT — $40.00For 3 x 12 AWG THHN conductors in EMT conduit, the smallest NEC-compliant size is 1/2" at 13.1% fill (limit: 40%). You need 10 sticks for a 100 ft run, costing $40.00.

Consider UpsizingWhile 1/2" conduit meets NEC fill limits, many electricians prefer 3/4" for easier wire pulling and future capacity. The cost difference is often minimal.

Fill calculations are based on NEC Chapter 9 Tables 4 and 5. Actual wire areas may vary by manufacturer. Always verify with local code requirements and consult a licensed electrician for permitted work.