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Conduit Fill Calculator

Choose a supported EMT trade size and enter copper THHN/THWN-2 groups as AWG:quantity. The calculator looks up its versioned subset of listed areas; an advanced mode accepts custom conductor and raceway areas.

Inputs

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* Required

Result

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Included conductors
3 × 12 AWG
Included conductors
3
Total conductor area
0.0399 in²
Raceway internal area
0.304 in²
Actual conduit fill
13.125 %
Common 2023 NEC fill limit
40 %
Maximum occupied area
0.1216 in²
Remaining area under this limit
0.0817 in²
Within common fill limit
Yes

How to use the Conduit Fill Calculator

Enter standard or custom mode; for standard mode, the 2023 edition, EMT trade size, and THHN/THWN-2 AWG:quantity groups.

Review adopted code edition, Chapter 9 table values, conductor insulation, nipples, grounding conductors, derating, and local amendments.

Read actual fill percentage, maximum fill percentage, maximum allowed area, remaining allowed area, and whether the layout is within the common fill limit.

Formula

Total conductor area = Σ(listed insulated-conductor area × quantity). Fill = conductor area ÷ EMT internal area × 100; the common limit is 53% for one conductor, 31% for two, or 40% for three or more.

Example

Three 12 AWG THHN/THWN-2 conductors occupy 0.0399 in² in 1/2 in EMT with 0.304 in² internal area, for 13.125% fill against the common 40% limit.

Assumptions and limitations

  • The built-in data is deliberately limited to a 2023 NEC subset for common EMT and copper THHN/THWN-2; verify the adopted edition, manufacturer listings, special cases, ampacity, derating, and installation requirements.
  • Conduit Fill Calculator treats the entered values as estimates and does not infer missing project, account, or personal details.
  • Calculations retain working precision except where the cited method requires an intermediate rounding step; displayed values are then formatted separately. Source rules and dated rates must be rechecked when they change.

Sources

Related electrical calculators

Frequently asked questions

How does the Conduit Fill Calculator work?

Total conductor area = Σ(listed insulated-conductor area × quantity). Fill = conductor area ÷ EMT internal area × 100; the common limit is 53% for one conductor, 31% for two, or 40% for three or more.

What information should I enter in the Conduit Fill Calculator?

Enter standard or custom mode; for standard mode, the 2023 edition, EMT trade size, and THHN/THWN-2 AWG:quantity groups, then verify adopted code edition, Chapter 9 table values, conductor insulation, nipples, grounding conductors, derating, and local amendments.

What should I verify before using this Conduit Fill Calculator result?

The built-in data is deliberately limited to a 2023 NEC subset for common EMT and copper THHN/THWN-2; verify the adopted edition, manufacturer listings, special cases, ampacity, derating, and installation requirements.

Reviewed 2026-08-14 · 2023-nec-emt-thhn-subset-v2 · content-2026-08-14 · Trusty Calculator Editorial Team