Conduit Fill Calculator

Calculate NEC-style raceway fill for EMT, PVC Schedule 40/80, RMC, IMC, and FMC with mixed THHN, XHHW, or THW conductors from 14 AWG through 750 kcmil.

Wire group 1

Total wire area: 0.013 in²

Enter conduit and conductor information to see fill results.

NEC Chapter 9 Table 1 planning limits: 1 conductor = 53%, 2 conductors = 31%, 3 or more conductors = 40%, and nipples 24 inches or shorter = 60%.

This is a planning calculator based on common NEC Chapter 9-style area tables. Final installations must be verified against the current NEC edition adopted locally, local amendments, ampacity derating, pulling tension, bend limits, and qualified electrical judgment.

Conduit Fill Formula

Fill % = total conductor area / conduit internal area x 100

Conduit fill compares the total cross-sectional area of all insulated conductors with the internal area of the raceway. The calculator multiplies each conductor area by quantity, totals mixed conductor groups, then compares the fill percentage with the standard or nipple limit.

SymbolVariableDescription
Total conductor areaWire areaThe selected conductor area multiplied by the quantity of that conductor group.
Conduit areaRaceway internal areaThe usable internal cross-sectional area for the selected conduit type and trade size.
Allowed fillFill limitCommon limits are 53% for one conductor, 31% for two, 40% for three or more, and 60% for nipples.

How to Use the Conduit Fill Calculator

  1. 1

    Choose conduit type and trade size

    Select EMT, PVC Schedule 40, PVC Schedule 80, RMC, IMC, or FMC, then choose a trade size from the available table.

  2. 2

    Choose the code basis and fill condition

    Use NEC raceway fill for typical U.S. work, CEC non-lead for Canadian non-lead conductors, or CEC lead-sheathed where that special rule applies. Use nipple only for raceway sections 24 inches or shorter.

  3. 3

    Add conductor groups

    For each conductor group, select THHN/THWN-2, XHHW, or THW, choose AWG or kcmil size, and enter quantity. Add another group for mixed sizes or insulation types.

  4. 4

    Review fill, area, and recommendation

    The result shows fill percentage, allowed fill, wire area, allowed area, remaining area, conductor breakdown, and the smallest trade size in the selected conduit type that passes.

  5. 5

    Export or print for documentation

    Use export to save a JSON result with timestamp, selected inputs, area values, status, and conductor breakdown.

Supported Conduit and Wire Tables

The calculator includes common internal raceway areas for EMT, PVC Schedule 40, PVC Schedule 80, RMC, IMC, and FMC, plus common Chapter 9-style conductor areas for THHN/THWN-2, XHHW, and THW from 14 AWG through 750 kcmil.

  • PVC Schedule 80 has less internal area than PVC Schedule 40 and often needs a larger trade size.
  • Mixed conductor pulls should be entered as separate wire groups so each insulation and size uses the right area.
  • FMC table coverage commonly stops at 4 inches in this calculator.
  • CEC lead-sheathed conductors use different fill limits: 55% for one, 30% for two, 40% for three, 38% for four, and 35% for more than four.

NEC Conduit Fill Limits

Use these planning limits to decide whether the selected raceway has enough internal area for the conductor count and installation condition.

ConditionMaximum fillWhen to use it
1 conductor53%Single conductor in a raceway.
2 conductors31%Two conductors in a raceway.
3 or more conductors40%Most branch circuits, feeders, and mixed pulls.
Nipple, 24 in. or less60%Short raceway sections where the nipple rule applies.
CEC lead-sheathed, 4 conductors38%Canadian lead-sheathed conductor condition.
CEC lead-sheathed, more than 435%Canadian lead-sheathed conductor condition.

Before You Pull Wire

A passing fill percentage does not automatically mean the installation is compliant. Check ampacity adjustment, voltage drop, equipment grounding conductor sizing, box fill, raceway bend count, pulling tension, wet-location insulation rating, temperature limits, and local amendments.

How to Choose the Right Conduit Size

A useful conduit fill result should help you decide what to install, not just show a percentage. Review the fill math, the minimum passing trade size, remaining capacity, and practical pulling risk before choosing the raceway.

  • Show both percent fill and square-inch area math so users can verify the result.
  • Recommend the minimum passing trade size when the selected conduit fails.
  • Tell the user how many same-size conductors the selected raceway can hold and how many more could be added.
  • Provide a result export or print path for field notes and plan review.

Conduit Fill Calculator FAQ

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