Calculator
Electrical Conduit Fill Calculator
Verify raceway fill before you pull, choose conduit type and trade size, add a row per conductor size and insulation, and get the fill percentage checked against the NEC Chapter 9 Table 1 limit, plus the smallest trade size that holds the bundle. Free, no signup.
Free
Conductors in the racewayAdd a row per conductor size and insulation, including the equipment grounding conductor, NEC Chapter 9 Note 3 requires it to be counted in the fill.
| Insulation | Size | Qty | Area | Remove |
|---|---|---|---|---|
| 0.1197 | ||||
| 0.0211 |
Run typeOnly change this for a short nipple between enclosures, it raises the fill limit to 60%.
NEC Chapter 9, Note 4: a conduit or tubing nipple no longer than 24 in., not including connectors, run between boxes, cabinets, or similar enclosures may be filled to 60%, and the 310.15(C)(1) bundling adjustment does not apply.
EMT 3/4"Article 358
Conduit fill
26.4%
10 conductors · 0.1408 in² of 0.533 in² interior area
0%NEC limit 40%100% (solid)
Passes NEC fillOver 2 conductors, 40% max fill · NEC Ch. 9, Table 1
Smallest EMT that passes3/4"
Fill at a glance
Conductor area used
0.1408 in²10 conductors · NEC Ch. 9 Table 5
Allowed fill area
0.213 in²40% of the interior area, over 2 conductors, 40% max fill
Conduit interior area
0.533 in²EMT 3/4" · NEC Ch. 9 Table 4
Remaining capacity
0.0722 in²Room left under the code limit
Room for
3 more10 AWG THHN / THWN / THWN-2 at the 40% limit
Minimum trade size
3/4"Smallest EMT in Table 4 that holds this pull
Every EMT trade sizeSame conductors, every trade size NEC Table 4 lists for this raceway, so you can see exactly what the next size up buys you.
| Trade size | Fill | Allowed (40%) | Status |
|---|---|---|---|
| 1/2" | 46.3% | 0.122 | Over |
| 3/4"selected | 26.4% | 0.213 | Passesminimum |
| 1" | 16.3% | 0.346 | Passes |
| 1-1/4" | 9.4% | 0.598 | Passes |
| 1-1/2" | 6.9% | 0.814 | Passes |
| 2" | 4.2% | 1.342 | Passes |
| 2-1/2" | 2.4% | 2.343 | Passes |
| 3" | 1.6% | 3.538 | Passes |
| 3-1/2" | 1.2% | 4.618 | Passes |
| 4" | 1.0% | 5.901 | Passes |
NEC notes
- Equipment grounding and bonding conductors count toward fill (NEC Ch. 9, Note 3), add them as their own row. Note 3 requires their actual dimensions, insulated or bare.
Industry benchmarks
- 1 conductor53%NEC Ch. 9 Table 1, a lone conductor may occupy 53% of the raceway.
- 2 conductors31%Two conductors bind against each other, so Table 1 drops the limit to 31%.
- 3 or more40%The everyday number, almost every real pull lands on the 40% column.
- Nipple ≤ 24 in.60%Note 4: short nipples between enclosures may be filled to 60%.
What you'll get
Pick the raceway
Choose conduit type, EMT, ENT, FMC, IMC, LFNC-A/B, LFMC, RMC, PVC Schedule 40 or 80, and trade size. Interior areas come straight from NEC Chapter 9 Table 4.
Add every conductor
Add a row per insulation type and AWG/kcmil size with a quantity, including the equipment grounding conductor, which NEC Chapter 9 Note 3 requires you to count. Areas come from Table 5.
Read the fill and the next size up
Get fill percentage with PASS or FAIL against the applicable 53%, 31%, 40% or 60% nipple limit, total conductor area, allowed fill area, remaining capacity in square inches, and a table comparing every trade size for that raceway.
How it works
- 1
Pick the raceway
Choose conduit type, EMT, ENT, FMC, IMC, LFNC-A/B, LFMC, RMC, PVC Schedule 40 or 80, and trade size. Interior areas come straight from NEC Chapter 9 Table 4.
- 2
Add every conductor
Add a row per insulation type and AWG/kcmil size with a quantity, including the equipment grounding conductor, which NEC Chapter 9 Note 3 requires you to count. Areas come from Table 5.
- 3
Read the fill and the next size up
Get fill percentage with PASS or FAIL against the applicable 53%, 31%, 40% or 60% nipple limit, total conductor area, allowed fill area, remaining capacity in square inches, and a table comparing every trade size for that raceway.
How the NEC decides how many wires fit in a conduit
Conduit fill is a cross-sectional area problem, not a wire count. NEC Chapter 9 Table 1 caps how much of a raceway’s interior the conductors may occupy: 53% for a single conductor, 31% for exactly two, and 40% for three or more. The two-conductor case is the strictest because two round conductors bind against each other in a bend, which is why adding a third conductor can make a pull legal that two would not be. A conduit or tubing nipple no longer than 24 inches between boxes or cabinets is permitted 60% fill under Note 4, and the 310.15(C)(1) bundling adjustment does not apply to it.
This calculator implements the full Chapter 9 chain: Table 4 interior areas for ten raceway types from 3/8 inch to 6 inch, Table 5 conductor areas for THHN/THWN-2, XHHW/XHHW-2, TW/THW/THHW/THW-2 and both RHH/RHW variants from 14 AWG to 1000 kcmil, and Note 7 rounding, where all conductors are the same size, a calculated decimal of 0.8 or larger rounds up to the next whole conductor. That last rule is where most online fill calculators go wrong: it means an all-same-size pull can sit slightly past the raw area limit and still be code-compliant, which is exactly how NEC Annex C arrives at its published counts. This tool reproduces 1,424 Annex C rows across EMT, IMC, RMC and PVC Schedule 40 and 80.
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Conduit Fill Calculator FAQs
NEC Chapter 9 Table 1 sets the limit by conductor count: 53% of the conduit’s interior area for one conductor, 31% for two, and 40% for three or more. A conduit or tubing nipple no longer than 24 inches installed between boxes, cabinets, or similar enclosures may be filled to 60%. The percentages apply to total cross-sectional area including insulation, not to the number of wires.
Two round conductors in a raceway tend to bind and wedge against each other as they round a bend, so NEC Table 1 drops the allowance to 31%, lower than either the 53% single-conductor case or the 40% three-or-more case. It is counter-intuitive but it is what the table says, and it means a two-wire pull sometimes needs a larger conduit than the same wires plus a third.
Yes. NEC Chapter 9 Note 3 requires equipment grounding and bonding conductors to be included when calculating conduit fill, using their actual dimensions whether insulated or bare. Add the EGC as its own row. This is different from ampacity derating, where the equipment grounding conductor is not counted as a current-carrying conductor.
It implements NEC (NFPA 70) 2023 Chapter 9, Table 1 percent fill and its Notes, Table 4 raceway dimensions, and Table 5 insulated conductor areas. Those values are unchanged from the 2011 edition through 2023 for every conduit type and insulation modelled here, so results are valid across recent code cycles. Results are a design aid only: your local authority having jurisdiction (AHJ) governs, adopted code editions and local amendments vary by state and municipality, and a licensed electrician should confirm the installation.
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