NEC calculators

Conduit fill calculator (NEC Chapter 9)

Check any mix of conductors, including compact and bare ones, in 14 raceway types, find the smallest trade size that works, or list the most of one conductor each trade size takes, edition by edition.

Calculated with electrician.wiki · https://electrician.wiki/calculators/conduit-fill/

Code / standard

Calculate

Raceway

Trade size (metric designator)

* = single-source dimensions (EMT 5 and 6).

Nipple of 24 in or less (60 % fill)

Conductors

Phase, neutral and switch legs.

Type

Size

More conductors

Type

Size

More conductors

Type

Size

Grounding (EGC)

Equipment grounding or bonding conductors.

EGC type

EGC size

Result · NEC 2023

27.3 % fill · OK (limit 40 %)

4 × 10 AWG THHN, 3 × 12 AWG THHN, 1 × 10 AWG THHN (EGC) take 27.3 % of 3/4 EMT (0.533 in²); the limit for more than two conductors is 40 %, so it passes under the NEC 2023. 3/4 is also the smallest EMT that works.

Fill: 27.3 %
Limit (8 conductors): 40 %
Conductor area: 0.1454 in²
Allowed in 3/4: 0.2132 in²
Smallest EMT that works: 3/4 (21)
Conductors (EGCs included): 8

Fill is only half the job: with more than three current-carrying conductors in the raceway, reduce their ampacity by the adjustment factors of 310.15(C)(1) (a neutral that carries only unbalanced current and the EGC don’t count).

Show the work

1. Conductor area (Chapter 9, Table 5)
$A = 4 \cdot 0.0211 in² + 3 \cdot 0.0133 in² + 1 \cdot 0.0211 in² = 0.1454 in²$
4 × 10 AWG THHN: 0.0211 in² each (Table 5); 3 × 12 AWG THHN: 0.0133 in² each (Table 5); 1 × 10 AWG THHN (EGC): 0.0211 in² each (Table 5)
2. Fill of 3/4 EMT (Table 4: 0.533 in², inside diameter 0.824 in)
$fill = \frac{A}{A_{raceway}} = \frac{0.1454 in²}{0.533 in²} = 27.3 %$
3. Limit: 40 % for more than two conductors (Chapter 9, Table 1)
$A_{\max} = 0.4 \cdot A_{raceway} = 0.4 \cdot 0.533 in² = 0.2132 in²$
0.1454 in² ≤ 0.2132 in².
4. Smallest EMT that works
1/2 EMT: 40 % of 0.304 in² = 0.1216 in², too small. 3/4 EMT: 40 % of 0.533 in² = 0.2132 in², enough.

References: NEC Chapter 9, Table 1 (2023): fill limits; Notes 3, 4 and 7 · NEC Chapter 9, Table 4 (2023): EMT areas · NEC Chapter 9, Table 5 (2023): insulated conductors · NEC 358.22 (2023): number of conductors in the raceway

Conductor areas are the approximate Table 5 values (Table 5A for compact, Table 8 for bare); Note 10 lets you use a manufacturer’s actual dimensions instead.
Equipment grounding and bonding conductors count toward fill at their actual size (Chapter 9, Table 1, Note 3).
Single conductors only. A multiconductor cable counts as one conductor of its outside diameter (Note 9), which this calculator does not model.
Types that Table 5 doesn’t list (USE-2, XHHN, XHWN, XHWN-2) need the manufacturer’s dimensions.
The drawing is to scale; the packing is a heuristic and only illustrates how the conductors might lie.

Report a problem with this result

How to use the conduit fill calculator

Pick the NEC edition you work to, then the raceway type and trade size. In Check fill mode, enter up to three groups of conductors (how many, the insulation type and the size) plus the equipment grounding conductors, which count toward fill like any other wire. The calculator returns the percentage of the raceway’s inside area the conductors take, the limit that applies to that number of conductors, a pass or fail, and the smallest trade size of the same raceway type that would work. The cross-section is drawn to scale: the circle is the raceway’s inside diameter from Chapter 9 Table 4 and every conductor is drawn at its Table 5 diameter, so you can see how crowded a pull will be.

Max conductors mode answers the other everyday question: how many conductors of one type and size fit in each trade size. It builds the answer the same way Informative Annex C does, from the Table 1 percentages and the Note 7 round-up, so it works for combinations Annex C doesn’t print, such as compact aluminum conductors in PVC Schedule 80 or bare conductors in flexible conduit. Turn on the nipple option for a raceway of 24 in. or less between two enclosures, which may be filled to 60 %.

The fill rules in Chapter 9

Raceway fill is a ratio of areas. Add up the cross-sectional area of every conductor, insulation included, and divide by the inside area of the raceway:

fill = \frac{A}{A_{raceway}} = \frac{n_{1} \cdot a_{1} + n_{2} \cdot a_{2} + …}{A_{raceway}}

Chapter 9 Table 1 sets the limit by the number of conductors: 53 % for one, 31 % for two and 40 % for three or more. The two-conductor limit is the lowest because a pair of large conductors lies side by side across most of the raceway’s diameter and binds easily in bends. The notes to the tables add the details that decide real jobs:

Equipment grounding and bonding conductors count, at their actual size, insulated or bare (Note 3).
Nipples of 24 in. or less between boxes, cabinets and similar enclosures may be filled to 60 %, and the ampacity adjustment factors don’t apply to them (Note 4). From 2023 the note says the length excludes the connectors.
Same-size conductors round up at 0.8 (Note 7). When every conductor has the same total area, divide the allowed area by one conductor; a decimal of 0.8 or more counts as the next whole conductor.
Bare conductors use the Table 8 dimensions (Note 8; the 2026 wording says so outright).
Cables such as a multiconductor cable count as one conductor sized by their major diameter (Note 9).
Table 5 dimensions are worst case (Note 10); compact-stranded conductors use Table 5A, and a manufacturer’s actual dimensions may be used instead.

Note 7 in symbols, for identical conductors of area a in a raceway of area A:

N_{\max} = \frac{0.4 \cdot A_{raceway}}{a}

If that gives fewer than three, the calculator checks two conductors at 31 % and one at 53 %, each with the same round-up. That ladder is why six 8 AWG THHN go in 3/4 EMT: 40 % of 0.533 in² is 0.2132 in², which divided by 0.0366 in² is 5.83, so the sixth conductor is allowed even though six of them fill 41.2 %.

Worked examples

Two circuits and a ground in 3/4 EMT

Four 10 AWG and three 12 AWG THHN, plus a 10 AWG insulated equipment grounding conductor: a mixed pull, so the plain 40 % limit applies.

1. Conductor area (Chapter 9, Table 5)
$A = 4 \cdot 0.0211 in² + 3 \cdot 0.0133 in² + 1 \cdot 0.0211 in² = 0.1454 in²$
2. Fill of 3/4 EMT (Table 4: 0.533 in², inside diameter 0.824 in)
$fill = \frac{A}{A_{raceway}} = \frac{0.1454 in²}{0.533 in²} = 27.3 %$
3. Limit: 40 % for more than two conductors (Chapter 9, Table 1)
$A_{\max} = 0.4 \cdot A_{raceway} = 0.4 \cdot 0.533 in² = 0.2132 in²$
4. Smallest EMT that works
1/2 EMT: 40 % of 0.304 in² = 0.1216 in², too small. 3/4 EMT: 40 % of 0.533 in² = 0.2132 in², enough.

Six 8 AWG THHN in 3/4 EMT (the 0.8 rule)

All six conductors are the same size, so Note 7 applies and the count rounds up.

1. Conductor area (Chapter 9, Table 5)
$A = 6 \cdot 0.0366 in² = 0.2196 in²$
2. Fill of 3/4 EMT (Table 4: 0.533 in², inside diameter 0.824 in)
$fill = \frac{A}{A_{raceway}} = \frac{0.2196 in²}{0.533 in²} = 41.2 %$
3. Limit: 40 % for more than two conductors (Chapter 9, Table 1)
$A_{\max} = 0.4 \cdot A_{raceway} = 0.4 \cdot 0.533 in² = 0.2132 in²$
4. All conductors are the same size: Note 7 (decimal of 0.8 or more rounds up)
$\frac{A_{40 %}}{a} = \frac{0.2132 in²}{0.0366 in²} = 5.83$
5. Smallest EMT that works
1/2 EMT: 40 % of 0.304 in² = 0.1216 in², too small. 3/4 EMT: 40 % of 0.533 in² = 0.2132 in², enough (with Note 7).

6 × 8 AWG THHN take 41.2 % of 3/4 EMT (0.533 in²); the limit for more than two conductors is 40 %, so it passes by the Note 7 round-up under the NEC 2023. 3/4 is also the smallest EMT that works.

A 200 A feeder in PVC Schedule 40

Four 3/0 AWG THHN with a 6 AWG bare copper equipment grounding conductor, which takes its Table 8 area.

1. Conductor area (Chapter 9, Table 5 and Table 8)
$A = 4 \cdot 0.2679 in² + 1 \cdot 0.027 in² = 1.099 in²$
2. Fill of 2 PVC Schedule 40 (Table 4: 3.291 in², inside diameter 2.047 in)
$fill = \frac{A}{A_{raceway}} = \frac{1.099 in²}{3.291 in²} = 33.4 %$
3. Limit: 40 % for more than two conductors (Chapter 9, Table 1)
$A_{\max} = 0.4 \cdot A_{raceway} = 0.4 \cdot 3.291 in² = 1.316 in²$
4. Smallest PVC Schedule 40 that works
1-1/2 PVC Schedule 40: 40 % of 1.986 in² = 0.7944 in², too small. 2 PVC Schedule 40: 40 % of 3.291 in² = 1.316 in², enough.

4 × 3/0 AWG THHN, 1 × 6 AWG bare stranded (EGC) take 33.4 % of 2 PVC Schedule 40 (3.291 in²); the limit for more than two conductors is 40 %, so it passes under the NEC 2023. 2 is also the smallest PVC Schedule 40 that works.

Compact aluminum in 2 in EMT

Four 4/0 compact XHHW-2 aluminum conductors use the smaller Table 5A dimensions.

1. Conductor area (Chapter 9, Table 5A)
$A = 4 \cdot 0.2733 in² = 1.093 in²$
2. Fill of 2 EMT (Table 4: 3.356 in², inside diameter 2.067 in)
$fill = \frac{A}{A_{raceway}} = \frac{1.093 in²}{3.356 in²} = 32.6 %$
3. Limit: 40 % for more than two conductors (Chapter 9, Table 1)
$A_{\max} = 0.4 \cdot A_{raceway} = 0.4 \cdot 3.356 in² = 1.342 in²$
4. All conductors are the same size: Note 7 (decimal of 0.8 or more rounds up)
$\frac{A_{40 %}}{a} = \frac{1.342 in²}{0.2733 in²} = 4.91$
5. Smallest EMT that works
1-1/2 EMT: 40 % of 2.036 in² = 0.8144 in², too small. 2 EMT: 40 % of 3.356 in² = 1.342 in², enough (with Note 7).

4 × 4/0 AWG compact XHHW take 32.6 % of 2 EMT (3.356 in²); the limit for more than two conductors is 40 %, so it passes under the NEC 2023. 2 is also the smallest EMT that works.

How many 12 AWG THHN fit in each EMT size

Max conductors mode: one conductor type and size, every trade size.

1. More than two conductors: 40 % of the raceway area (Table 1), divided by one conductor (Table 5)
$\frac{0.4 \cdot A_{raceway}}{a} = \frac{0.4 \cdot 0.533 in²}{0.0133 in²} = 16.03$
2. Every EMT trade size
1/2: 9 · 3/4: 16 · 1: 26 · 1-1/4: 45 · 1-1/2: 61 · 2: 101 · 2-1/2: 176 · 3: 266 · 3-1/2: 347 · 4: 443 · 5: 608* · 6: 877*

3/4 EMT takes up to 16 12 AWG THHN conductors under Chapter 9 Table 1 (40 %, NEC 2023); 1/2 takes 9, 1 takes 26, 1-1/4 takes 45, 1-1/2 takes 61.

A larger job from EC&M’s raceway fill primer checks the same way: 45 × 12 AWG plus 15 × 14 AWG THHN is 0.744 in² of conductor, so trade size 1-1/4 EMT (0.5984 in² at 40 %) is too small and 1-1/2 EMT (0.8144 in²) is the smallest that works. Sixty circuit conductors in one raceway is a fill answer only; their ampacity would have to be adjusted heavily, which is why such pulls are usually split.

How many conductors fit in EMT

The table below is computed by the calculator for THHN, THWN and THWN-2, the most common building wire. Use it for a single size; for a mix of sizes, or anything with a ground wire of a different size, run Check fill instead, because Note 7 applies only when every conductor is the same size.

Most THHN/THWN-2 conductors of one size in EMT, computed by the calculator (Table 1 limits with the Note 7 round-up, NEC 2023).
EMT trade size	40 % area	14 AWG	12 AWG	10 AWG	8 AWG	6 AWG
1/2	0.1216 in²	12	9	5	3	2
3/4	0.2132 in²	22	16	10	6	4
1	0.3456 in²	35	26	16	9	7
1-1/4	0.5984 in²	61	45	28	16	12
1-1/2	0.8144 in²	84	61	38	22	16
2	1.342 in²	138	101	63	36	26

Insulation type changes the answer more than people expect. XHHW is fatter than THHN in the small sizes, so 3/4 EMT takes 10 × 10 AWG THHN but only 8 × 10 AWG XHHW. RHH and RHW with an outer covering are larger still. Pick the exact type on the label, not the one you usually buy.

Same trade size, different raceway

A trade size is a name, not a dimension. Each raceway type has its own wall thickness and so its own inside area, which is why Table 4 lists them separately. PVC Schedule 80 has the thickest wall and the least room: trade size 1 takes 20 × 12 AWG THHN against 25 in Schedule 40. Where a run changes from Schedule 40 underground to Schedule 80 where it is exposed to damage, size the whole run for the Schedule 80 section.

Trade size 1 in every raceway type that lists it: inside diameter and area from Chapter 9 Table 4, and the most 12 AWG THHN each one takes.
Raceway, trade size 1	Inside Ø	Total area	40 % of it	12 AWG THHN
EMT	1.049 in	0.864 in²	0.3456 in²	26
ENT	1.029 in	0.832 in²	0.3328 in²	25
FMC	1.02 in	0.817 in²	0.3268 in²	24
IMC	1.105 in	0.959 in²	0.3836 in²	29
RMC	1.063 in	0.887 in²	0.3548 in²	26
LFMC	1.054 in	0.873 in²	0.3492 in²	26
PVC Schedule 40	1.029 in	0.832 in²	0.3328 in²	25
PVC Schedule 80	0.936 in	0.688 in²	0.2752 in²	20

Since the 2017 edition ENT has used the PVC Schedule 40 inside dimensions; charts based on the 2011 NEC show smaller ENT areas and give lower counts. HDPE conduit also shares the Schedule 40 values. Trade size 3/8 flexible metal conduit has its own conductor table in 348.22 as well, which depends on whether the fittings sit inside or outside the conduit.

What changes from 2017 to 2026

The Table 1 percentages, the Table 5 conductor areas and almost every Table 4 dimension are the same in all four editions, so most results don’t change with the edition. The differences are at the edges:

EMT and IMC trade sizes 5 and 6 were added in 2023, with the maximum trade size for both raised from 4 to 6. Under the 2017 and 2020 editions the calculator stops EMT at trade size 4. The EMT 5 and 6 dimensions here come from a single source, NFPA’s 2023-cycle First Revision working text, and equal the RMC values, so results that use them carry a warning. The IMC 5 and 6 dimensions were not in any public NFPA record we could check, so those sizes are left out rather than guessed.
Nipple length. From 2023, Note 4 says the 24 in. is measured without the connectors.
Note 7 and cables. The 2026 edition extends the 0.8 round-up to cables, including the single-cable case, and states that bare conductors use Table 8.
PVC larger than trade size 6. 2026 permits it underground, but Table 4 still stops at 6, so larger sizes need the manufacturer’s inside diameter.
Ampacity adjustment section. The more-than-three-conductors factors are 310.15(B)(3)(a) in 2017 and 310.15(C)(1) from 2020; the warnings cite the right one for the edition you pick.

Common mistakes

Leaving out the ground wire. Note 3 counts it. In the 3/4 EMT example it adds 0.0211 in², and on a full raceway that is the difference between pass and fail.
Using 40 % for two conductors. Two conductors are limited to 31 %. A pair of 6 AWG THHN in 1/2 EMT passes only because Note 7 rounds 1.86 up to 2.
Applying the 0.8 rule to a mix. It applies only when every conductor has the same area; a mixed fill is checked against the plain percentage.
Reading Annex C for the wrong insulation or raceway. Each Annex C table is for one raceway type and one insulation group. The calculator removes that risk by computing from the type you choose.
Sizing a feeder raceway before adding its EGC. Three 3/0 AWG THHN for a 200 A three-phase feeder fit 1-1/2 EMT; add the 6 AWG insulated equipment grounding conductor and the smallest that works is 2.
Treating fill as the only limit. More than three current-carrying conductors in a raceway need ampacity adjustment, which usually limits branch-circuit raceways long before 40 % does. Size the conductors with the ampacity calculator or the wire size calculator first.
Pulling three conductors at a jam ratio. When the raceway’s inside diameter is 2.8 to 3.2 times the conductor diameter, three conductors can wedge at a bend; the calculator warns when that happens.

Method and verification

Areas come from NEC Chapter 9: Table 4 for the raceway (total internal area, the 100 % column), Table 5 for insulated conductors, Table 5A for compact conductors and Table 8 for bare conductors. The limit is the Table 1 percentage of the exact Table 4 area, not the rounded percentage columns, and a fill passes when the conductor area is at or below it, or, for same-size conductors, when the count is at or below the Note 7 result. Every value was cross-checked against at least two independent transcriptions of the code tables.

The tests reproduce EC&M’s worked raceway fill example, the Annex C counts for THHN in EMT from 1/2 to 2 in (for example 9 × 12 AWG in trade size 1/2 and 16 in 3/4), every branch of the 0.8 rule, the 60 % nipple limit, the edition rules for EMT and IMC trade sizes 5 and 6, and properties such as “more conductors never lower the fill” and “the smallest trade size passes and the one below it fails”. The drawing’s packing routine is checked for overlaps on hundreds of circles. Next in the workflow: check the boxes at each end with the box fill calculator.

Covers single conductors in Chapter 9 raceways; multiconductor cables and cable tray are not modeled. Updated 2026-10-14. Found a problem? Report it and we log every fix publicly.

Questions people ask

How do you calculate conduit fill?

Add the cross-sectional areas of all the conductors, insulation and ground wires included (Chapter 9 Table 5, 5A or 8), and divide by the raceway’s inside area from Table 4. Compare the result with Table 1: 53 % for one conductor, 31 % for two, 40 % for three or more.

What is the maximum conduit fill percentage?

40 % for three or more conductors, 31 % for two and 53 % for one (NEC Chapter 9, Table 1). A nipple of 24 in. or less between enclosures may be filled to 60 %.

How many 12 AWG wires can go in 1/2 EMT?

Nine 12 AWG THHN: 40 % of 0.304 in² is 0.1216 in², and each conductor is 0.0133 in². In 3/4 EMT the answer is 16. Remember that a ground wire counts as one of them.

Do ground wires count in conduit fill?

Yes. Chapter 9 Table 1 Note 3 includes equipment grounding and bonding conductors, at their actual size, insulated or bare. Bare conductors use the Table 8 dimensions.

What is the 0.8 rule in conduit fill?

Note 7 to Chapter 9 Table 1: when all the conductors are the same size, divide the allowed area by one conductor’s area, and a decimal of 0.8 or more counts as one more conductor. That is why six 8 AWG THHN fit 3/4 EMT (5.83 rounds up to 6).

Can I fill conduit to 60 %?

Only a nipple: a raceway of 24 in. or less between boxes, cabinets or similar enclosures (Note 4), not counting the connectors from 2023. The ampacity adjustment factors don’t apply to such a nipple.