What fill percentage does the NEC allow?

NEC 2023 Chapter 9 Table 1 permits: 53% for one conductor, 31% for two conductors, and 40% for three or more conductors. This calculator automatically applies the correct limit based on total conductor count.

Which conduit types are included?

EMT (Electrical Metallic Tubing), IMC (Intermediate Metal Conduit), and RMC (Rigid Metal Conduit). Each has different internal diameters, so the fill area differs even at the same trade size.

What conductor sizes are supported?

AWG 14 through 4/0, plus 250, 300, 350, 400, 500, 600, 700, 750, 1000 kcmil — the full range from NEC 2023 Chapter 9 Table 5 (THHN/THWN-2 compact area).

Are these THHN/THWN values?

Yes. Conductor cross-section areas use NEC Table 5 values for THHN/THWN-2 insulation, the most common wire type. For other insulation types (XHHW, RHH, etc.) the area differs; consult NEC Table 5 for exact values.

Can I mix different AWG sizes in one conduit?

Yes. Add a row for each conductor size and enter the quantity. The calculator sums all conductor areas before computing the fill percentage.

Conduit Fill Calculator

Name: Conduit Fill Calculator
Availability: InStock
Author: Nham Vu

Select conduit type and trade size, add conductors by AWG, and instantly see the fill percentage against NEC 2023 limits.

Conduit Configuration

Conduit Type

Trade Size

Conductors

Fill Result

Configure conduit and add conductors, then click Calculate Fill.

NEC 2023 Chapter 9, Table 1 — Fill Limits

53%

1 conductor

31%

2 conductors

40%

3+ conductors

Summary

Select conduit type and trade size, add conductors by AWG, and instantly see the fill percentage against NEC 2023 limits.

How it works

Select the conduit type: EMT, IMC, or RMC.
Pick the trade size (½" through 4") from the dropdown.
Add each conductor group: choose AWG size and enter the quantity.
The calculator sums the total conductor area and divides by the conduit internal area.
Compare the result against NEC 2023 Chapter 9 Table 1 limits (40% for 3+ conductors, 53% for 2, 100% for 1).
Adjust conductor count or trade size until the fill is within the allowed limit.

Use cases

Verify a panel feeder conduit is not over-filled before pulling wire.
Size a new conduit run for a given set of branch circuit conductors.
Check compliance when adding circuits to an existing conduit.
Quickly compare EMT vs. RMC fill for the same conductor bundle.
Confirm a homerun conduit meets NEC 40% fill rule before rough-in.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu