Conduit Fill Calculator
Choose the raceway
Select the raceway family and trade size shown on the product or plans.
Check the area occupied by one uniform group of copper THHN/THWN-2 conductors in EMT, IMC, RMC, PVC Schedule 40 or PVC Schedule 80. Select the raceway and trade size, then enter one wire size and a count from 1 to 200. The calculator reports used area, permitted area, actual fill percentage, remaining permitted area and the maximum count supported by its tables.
How to calculate conduit fill
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1
Choose the raceway
Select EMT, IMC, RMC, PVC Schedule 40 or PVC Schedule 80 and the applicable trade size.
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2
Enter the conductor group
Choose one copper THHN/THWN-2 size from 14 AWG through 4/0 and enter a count from 1 to 200.
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3
Review every result
Compare used and permitted area, fill percentage, remaining area and maximum count, then verify the installation under the adopted code.
How the fill calculation works
Conduit fill compares the combined cross-sectional area of the insulated conductors with the raceway’s internal area. This calculator uses tabulated areas for common trade sizes of EMT, IMC, RMC, PVC Schedule 40 and PVC Schedule 80, together with the insulated area of copper THHN/THWN-2 from 14 AWG through 4/0.
For a single uniform group:
used area = conductor count × area of one insulated conductor
actual fill % = used area ÷ raceway internal area × 100
The permitted percentage changes with the number of conductors under NEC Chapter 9, Table 1:
| Number of conductors | Maximum cross-sectional fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| 3 or more | 40% |
Southwire’s conduit-fill guidance summarizes the same NEC percentages, while the NFPA public-access code portal provides access to the adopted table context. Permitted area is the raceway area multiplied by the applicable percentage. Remaining area is permitted area minus used area; a negative value means the selected group exceeds the tabulated limit.
Worked example
Suppose a run uses 3/4-inch EMT with nine 10 AWG copper THHN/THWN-2 conductors. The tabulated EMT area is 0.533 in² and the tabulated area of one conductor is 0.0211 in².
used area = 9 × 0.0211 = 0.1899 in²
Because there are more than two conductors, the permitted area is 0.533 × 40% = 0.2132 in². The actual fill is about 35.63%, leaving about 0.0233 in² before the permitted-area limit. At that raceway and wire size, the tabulated capacity is 10 conductors. Manufacturer calculators such as Encore Wire’s raceway-fill calculator are useful cross-checks.
Scope and code check
This result covers one conductor size and insulation type only. It does not calculate mixed conductor groups, ampacity, adjustment or correction factors, grounding-conductor sizing, box fill, pull difficulty, bend limits or jamming. Equipment grounding or bonding conductors present in the raceway still count toward fill. Confirm conductor and raceway markings, the locally adopted NEC edition, amendments and manufacturer data with the authority having jurisdiction or a qualified electrical professional before installation.
Frequently Asked Questions
NEC Chapter 9, Table 1 permits 53% of the raceway cross section for one conductor, 31% for two and 40% for more than two under the table’s scope.
It is the maximum number of the selected uniform THHN/THWN-2 conductor size that the chosen raceway and trade-size table can accommodate under the applicable fill percentage. It is not an ampacity or derating result.
The calculator uses Livewire, so selected values are sent to this site to update results. Funnel mode may also place non-sensitive values in the page URL. Do not enter confidential information.
No. Verify the adopted electrical code, local amendments, listed raceway and conductor dimensions, grounding conductors and all other design requirements with the authority having jurisdiction or a qualified electrical professional.
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