How many wires can fit in a conduit?

It depends on the conduit type and trade size, and the size and insulation of the wires. The limit is a share of the conduit's cross-section: 53% for one conductor, 31% for two and 40% for more than two (NEC Chapter 9, Table 1). For EMT 3/4 in, that is 16 wires of 12 AWG THHN or 10 of 10 AWG THHN when all are the same size.

What is the NEC conduit fill formula?

Add the Table 5 area of every conductor, divide by the Table 4 internal area of the conduit and compare with the Table 1 limit. For the example: 0.1642 sq in ÷ 0.533 sq in = 30.81%, against a 40% limit.

Why are the limits 53%, 31% and 40%?

They are set by Table 1 of Chapter 9: 53% for one conductor, 31% for two and 40% for more than two. The limits leave room to pull the wire without damaging the insulation. Two conductors get the lowest percentage because that is the case where they can wedge side by side as they are pulled.

What is Note 7 and when do I round up?

When you work out the maximum number of conductors of the same size and type, and the result has a decimal of 0.8 or more, Note 7 lets you use the next whole number. 1 in EMT with 12 AWG THHN gives 25.98: 25 without the rule, 26 with it. A result such as 12.54 (1/2 in EMT, 14 AWG THHN) stays at 12. It does not apply to mixed wire sizes, and this tool applies it only when the rounded count is 3 or more because sources do not settle whether it covers one and two conductors. Check how your inspector reads it.

What is the fill for a nipple?

Note 4 allows a conduit or tubing nipple of 24 in or less between boxes, cabinets or similar enclosures to be filled to 60% of its area. The sample conductors (20 wires, 0.3128 sq in) fill 3/4 in EMT 58.69%: a pass as a nipple, a fail as a run (limit 40%). Whether connectors count toward the 24 in changed between editions, so check yours.

Do equipment grounding conductors count?

Yes, in general. Where an equipment grounding conductor or bonding jumper is installed in the raceway it is counted in the fill, using its Table 5 area if insulated. This tool has no bare-wire option: bare conductors use Table 8 areas, so add an insulated ground as a row of its own and treat a bare ground separately.

Why does XHHW-2 take more room than THHN?

Its insulation is thicker. At 12 AWG, XHHW-2 is 0.0181 sq in against 0.0133 sq in for THHN/THWN-2, so fewer fit: 11 12 AWG XHHW-2 wires against 16 THHN in EMT 3/4 in. From 4 AWG up the difference is small, and XHHW-2 is slightly smaller than THHN.

Is PVC fill different from EMT?

The percentages are the same, but the internal areas differ, and Schedule 80 PVC has thicker walls and less room than Schedule 40. At 1 in, EMT has 0.864 sq in, PVC Schedule 40 0.832 and Schedule 80 0.688.

Does conduit fill take care of derating?

No. Fill is only about physical room. When more than three current-carrying conductors share a raceway, the ampacity adjustment factors in NEC 310.15(C)(1) reduce what each wire may carry, and the ambient temperature may reduce it again. Size the wire for ampacity first, then check the fill.

Are the numbers official?

They are the Chapter 9 values as reproduced by published sources, not copied from the NFPA text, and a few could not be fully confirmed (see "How the table values were checked"). Verify against the NEC edition your jurisdiction has adopted, and ask your inspector or a licensed electrician when it matters.

Is anything I enter stored or sent?

No. The calculation runs in your browser. Conduit types, wire sizes and counts are not stored or sent anywhere. The site records only that the tool was used, never the values.

Conduit Fill Calculator

10 THHN conductors (6 of 12 AWG and 4 of 10 AWG) in EMT 3/4 in take 0.1642 sq in, 30.81% of the conduit, under the 40% limit for more than two conductors: it passes with 0.0490 sq in to spare. Pick the conduit type and trade size, then list each wire size, insulation type and quantity: the calculator adds the NEC Chapter 9 Table 5 conductor areas, compares them with the Table 4 conduit area and the Table 1 limit (53%, 31% or 40%), and shows pass or fail and the most of each wire that would fit alone (16 of 12 AWG in the example). It is a planning aid built on published table values: check the edition of the NEC your authority having jurisdiction has adopted, and note that wire derating and ampacity are separate requirements.

Updated 2026-10-13Runs in your browser: nothing you enter is uploadedHow this tool works

Pass: 30.81% full (limit 40%)

10 conductors take 0.1642 sq in of the 0.2132 sq in allowed in EMT 3/4 in, leaving 0.0490 sq in.

Area of each conductor row in square inches and the most of that wire that would fit alone
Conductor	Qty	Each (sq in)	Row total (sq in)	Most of this wire alone
12 AWG THHN/THWN-2	6	0.0133	0.0798	16
10 AWG THHN/THWN-2	4	0.0211	0.0844	10

Conduit: EMT 3/4 in, 0.533 sq in total
Conductors: 10
Total conductor area: 0.1642 sq in
Fill limit: 40% (over 2 conductors)
Allowable area: 0.2132 sq in
Fill: 30.81%
Area to spare: 0.0490 sq in

The "most of this wire alone" column assumes that one wire size fills the whole conduit; Note 7 rounding is not applied to the mixed total above.

An estimate, not a design.

Areas come from NEC Chapter 9, Tables 1, 4 and 5 as reproduced by published sources, not from the NFPA text. A few values could not be fully confirmed: see "How the table values were checked" below.
Verify against the NEC edition your authority having jurisdiction has adopted, and ask your inspector or a licensed electrician when it matters.
Conductor derating and ampacity (NEC 310.15 and 310.16) are separate requirements that this tool does not check.

Fill limits: NEC Chapter 9, Table 1

The share of the conduit or tubing cross-section that conductors may fill. Note 4 allows 60% in a nipple of 24 in or less between boxes.
Conductors in the raceway	Maximum fill	Allowable area in the example (3/4 in EMT)
1	53%	0.2825 sq in
2	31%	0.1652 sq in
Over 2	40%	0.2132 sq in
Nipple of 24 in or less (Note 4)	60%	0.3198 sq in

Conduit internal area used: NEC Chapter 9, Table 4 (100%)

Total internal cross-sectional area in square inches. A dash means the size is not offered here: the Table 4 figures for it could not be confirmed (RMC 3-1/2 and 4 in) or it is a restricted-use size.
Trade size	EMT	RMC	PVC-40	PVC-80	FMC
1/2 in	0.304	0.314	0.285	0.217	0.317
3/4 in	0.533	0.549	0.508	0.409	0.533
1 in	0.864	0.887	0.832	0.688	0.817
1-1/4 in	1.496	1.526	1.453	1.237	1.277
1-1/2 in	2.036	2.071	1.986	1.711	1.858
2 in	3.356	3.408	3.291	2.874	3.269
2-1/2 in	5.858	4.866	4.695	4.119	4.909
3 in	8.846	7.499	7.268	6.442	7.069
3-1/2 in	11.545	—	9.737	8.688	9.621
4 in	14.753	—	12.554	11.258	12.566

Allowable area for more than two conductors (40%)

Table 4 total area × 0.40, in square inches, to three decimals. The printed table rounds each column itself, so a figure can differ from the book in the last digit.
Trade size	EMT	RMC	PVC-40	PVC-80	FMC
1/2 in	0.122	0.126	0.114	0.087	0.127
3/4 in	0.213	0.220	0.203	0.164	0.213
1 in	0.346	0.355	0.333	0.275	0.327
1-1/4 in	0.598	0.610	0.581	0.495	0.511
1-1/2 in	0.814	0.828	0.794	0.684	0.743
2 in	1.342	1.363	1.316	1.150	1.308
2-1/2 in	2.343	1.946	1.878	1.648	1.964
3 in	3.538	3.000	2.907	2.577	2.828
3-1/2 in	4.618	—	3.895	3.475	3.848
4 in	5.901	—	5.022	4.503	5.026

Conductor areas used: NEC Chapter 9, Table 5

Approximate area in square inches of one round, concentric-stranded conductor with its insulation. THHN, THWN and THWN-2 share a column, as do XHHW and XHHW-2. Compact-stranded wire (Table 5A) is smaller and is not included.
Size	THHN/THWN-2 (sq in)	XHHW-2 (sq in)
14 AWG	0.0097	0.0139
12 AWG	0.0133	0.0181
10 AWG	0.0211	0.0243
8 AWG	0.0366	0.0437
6 AWG	0.0507	0.0590
4 AWG	0.0824	0.0814
3 AWG	0.0973	0.0962
2 AWG	0.1158	0.1146
1 AWG	0.1562	0.1534
1/0 AWG	0.1855	0.1825
2/0 AWG	0.2223	0.2190
3/0 AWG	0.2679	0.2642
4/0 AWG	0.3237	0.3197
250 kcmil	0.3970	0.3904
300 kcmil	0.4608	0.4536
350 kcmil	0.5242	0.5166
400 kcmil	0.5863	0.5782
500 kcmil	0.7073	0.6984

Most THHN/THWN-2 wires of one size in EMT (over 2 conductors, Note 7 applied)

Table 4 area × 0.40 ÷ the Table 5 area, with a decimal of 0.8 or more rounded up to the next whole number (Note 7). Valid only when every conductor in the conduit is the same size and type.
EMT trade size	14 AWG	12 AWG	10 AWG	8 AWG	6 AWG	4 AWG
1/2 in	12	9	5	3	1	1
3/4 in	22	16	10	6	4	2
1 in	35	26	16	9	7	4
1-1/4 in	61	45	28	16	12	7
1-1/2 in	84	61	38	22	16	10
2 in	138	101	63	36	26	16
2-1/2 in	241	176	111	64	46	28
3 in	364	266	167	96	69	43
3-1/2 in	476	347	219	126	91	56
4 in	608	443	279	161	116	71

How the table values were checked

The NFPA 70 text itself could not be opened while this tool was built, so each value was compared with web reproductions of the tables (the 2017 Chapter 9 PDF, an ICC sample, the NECA/IBEW Table 4 sheet, PDHonline, Electriflex and Electrical Contractor material, forum posts and calculator sites). Southwire and Cerro Wire pages could not be reached. Anything not confirmed is flagged here.
Item	Status	Detail
Table 1 fill limits (53 %, 31 %, 40 %)	Confirmed	Stated the same way by every source found.
Note 4: nipples of 24 in or less may be filled to 60 %	Confirmed	Wording found for the 2017 and 2023 editions; whether the 24 in includes the connectors changed between editions.
Note 7: round up when the decimal is 0.8 or larger	Confirmed	Found in the 2011 and 2017 wording. The sources did not settle whether it applies to a result of 1 or 2 conductors, so the tool applies it only when the rounded count is 3 or more.
Table 4 PVC Schedule 40 areas, all sizes	Confirmed	Matched a full calculator reproduction.
Table 4 PVC Schedule 80 areas, all sizes	Confirmed	1-1/4 to 4 in matched a published chart; 1/2 and 3/4 in matched a second source.
Table 4 EMT areas, all sizes	Confirmed	1/2 to 3 in matched several sources; 3-1/2 and 4 in matched published internal diameters (3.834 and 4.334 in) and a 40 % value.
Table 4 RMC areas, 1/2 to 3 in	Confirmed	Matched a Table 4 reproduction and spot checks of 1/2, 3/4 and 2 in.
Table 4 RMC areas, 3-1/2 and 4 in	Left out	Sources disagreed (9.521 and 12.252 against 10.010 and 12.882 sq in) and none was authoritative, so these sizes are not offered.
Table 4 FMC areas	Partly confirmed	1/2 and 3/4 in matched two sources; 1 to 4 in matched one reproduction and another site disagreed on the 40 % column. Treat FMC as less certain. The 3/8 in size is not offered.
Table 5 THHN/THWN-2 areas, all sizes	Confirmed	Every size matched the 2017 Chapter 9 text, an ICC sample of the table or a code-calculation article; 400 kcmil (0.5863) appeared in only one of them.
Table 5 XHHW-2 areas, 14 AWG to 3/0 AWG and 250 to 500 kcmil	Confirmed	Matched the 2017 Chapter 9 text, PDHonline and calculator reproductions; 300, 350 and 400 kcmil came from a PDF with a garbled layout.
Table 5 XHHW-2 area, 4/0 AWG (0.3197)	Not confirmed	No source reproducing this one value was found. It fits between its neighbors, but treat it as unverified.
Compact-stranded wire (Table 5A)	Left out	Not included. Compact conductors have smaller areas than the standard values used here.

How to calculate conduit fill

Find the area of each conductor. Look up each wire size and insulation in NEC Chapter 9, Table 5. In the example, 12 AWG THHN is 0.0133 sq in and 10 AWG THHN is 0.0211 sq in, with the insulation included.
Add the areas. Multiply each area by its quantity and add: 6 × 0.0133 + 4 × 0.0211 = 0.1642 sq in. Count every current-carrying conductor and any insulated equipment grounding conductor.
Find the conduit area and the limit. Table 4 gives EMT 3/4 in a total internal area of 0.533 sq in. Table 1 allows 53% for one conductor, 31% for two and 40% for more than two, so the example may use 0.2132 sq in.
Compare. 0.1642 ÷ 0.533 = 30.81%, under 40%, so the fill passes. If it fails, go up a trade size, or split the conductors between two raceways.
Work out how many of one wire fit. For a conduit holding only one wire size, divide the allowable area by the wire's area: 0.2132 ÷ 0.0133 = 16.03, so 16 wires of 12 AWG THHN fit. Round down unless the decimal is 0.8 or more (Note 7).

Frequently asked questions

How many wires can fit in a conduit?: It depends on the conduit type and trade size, and the size and insulation of the wires. The limit is a share of the conduit's cross-section: 53% for one conductor, 31% for two and 40% for more than two (NEC Chapter 9, Table 1). For EMT 3/4 in, that is 16 wires of 12 AWG THHN or 10 of 10 AWG THHN when all are the same size.
What is the NEC conduit fill formula?: Add the Table 5 area of every conductor, divide by the Table 4 internal area of the conduit and compare with the Table 1 limit. For the example: 0.1642 sq in ÷ 0.533 sq in = 30.81%, against a 40% limit.
Why are the limits 53%, 31% and 40%?: They are set by Table 1 of Chapter 9: 53% for one conductor, 31% for two and 40% for more than two. The limits leave room to pull the wire without damaging the insulation. Two conductors get the lowest percentage because that is the case where they can wedge side by side as they are pulled.
What is Note 7 and when do I round up?: When you work out the maximum number of conductors of the same size and type, and the result has a decimal of 0.8 or more, Note 7 lets you use the next whole number. 1 in EMT with 12 AWG THHN gives 25.98: 25 without the rule, 26 with it. A result such as 12.54 (1/2 in EMT, 14 AWG THHN) stays at 12. It does not apply to mixed wire sizes, and this tool applies it only when the rounded count is 3 or more because sources do not settle whether it covers one and two conductors. Check how your inspector reads it.
What is the fill for a nipple?: Note 4 allows a conduit or tubing nipple of 24 in or less between boxes, cabinets or similar enclosures to be filled to 60% of its area. The sample conductors (20 wires, 0.3128 sq in) fill 3/4 in EMT 58.69%: a pass as a nipple, a fail as a run (limit 40%). Whether connectors count toward the 24 in changed between editions, so check yours.
Do equipment grounding conductors count?: Yes, in general. Where an equipment grounding conductor or bonding jumper is installed in the raceway it is counted in the fill, using its Table 5 area if insulated. This tool has no bare-wire option: bare conductors use Table 8 areas, so add an insulated ground as a row of its own and treat a bare ground separately.
Why does XHHW-2 take more room than THHN?: Its insulation is thicker. At 12 AWG, XHHW-2 is 0.0181 sq in against 0.0133 sq in for THHN/THWN-2, so fewer fit: 11 12 AWG XHHW-2 wires against 16 THHN in EMT 3/4 in. From 4 AWG up the difference is small, and XHHW-2 is slightly smaller than THHN.
Is PVC fill different from EMT?: The percentages are the same, but the internal areas differ, and Schedule 80 PVC has thicker walls and less room than Schedule 40. At 1 in, EMT has 0.864 sq in, PVC Schedule 40 0.832 and Schedule 80 0.688.
Does conduit fill take care of derating?: No. Fill is only about physical room. When more than three current-carrying conductors share a raceway, the ampacity adjustment factors in NEC 310.15(C)(1) reduce what each wire may carry, and the ambient temperature may reduce it again. Size the wire for ampacity first, then check the fill.
Are the numbers official?: They are the Chapter 9 values as reproduced by published sources, not copied from the NFPA text, and a few could not be fully confirmed (see "How the table values were checked"). Verify against the NEC edition your jurisdiction has adopted, and ask your inspector or a licensed electrician when it matters.
Is anything I enter stored or sent?: No. The calculation runs in your browser. Conduit types, wire sizes and counts are not stored or sent anywhere. The site records only that the tool was used, never the values.

How it works

Each conductor row is multiplied by its Table 5 area (square inches, insulation included) and the rows are summed. The conduit's Table 4 total area is multiplied by the Table 1 limit for the total number of conductors in the raceway: 53% for one, 31% for two, 40% for more than two, or 60% for a nipple of 24 in or less (Note 4). The fill is the total conductor area divided by the conduit's total area, and the result passes when the total conductor area does not exceed the allowable area. The "most of this wire alone" figure divides the 40% (or 60%) area by one conductor's area and rounds down, or up when the decimal is 0.8 or more (Note 7); a count of one or two is checked against the 53% and 31% limits instead. Areas are computed from the Table 4 totals rather than copied from its printed percentage columns, which are rounded to three decimals. Conductors are treated as round, standard-stranded wire; compact stranding, multiconductor cables, bare wire and conduit types other than the five offered (IMC, LFNC, rigid PVC Type A, HDPE and others) are not covered. This is an estimate, not a design or an inspection. Derating and ampacity (NEC 310.15 and 310.16) are separate requirements, as are box fill, bend and pull-length rules. Confirm every value against the NEC edition your authority having jurisdiction has adopted. How each table value was checked, and what could not be confirmed, is listed under "How the table values were checked".

Sources

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