How many wires fit in 4-inch EMT conduit?

A 4-inch EMT conduit has 14.753 square inches of internal area. With more than two conductors the NEC limits fill to 40%, or 5.901 in². That works out to 443 #12 THHN, 608 #14 THHN, 279 #10 THHN, or 161 #8 THHN conductors.

How many 12 AWG THHN wires fit in 4-inch EMT?

443 conductors. Each 12 AWG THHN wire is 0.0133 in² per NEC Chapter 9, Table 5, and the 40% fill area of 4-inch EMT is 5.901 in².

What is the maximum fill percentage for conduit?

NEC Chapter 9, Table 1 sets three limits: 53% for a single conductor, 31% for exactly two conductors, and 40% for three or more. The lower two-conductor figure exists because two round conductors pack poorly inside a round raceway.

Does the equipment grounding conductor count toward conduit fill?

Yes. Every conductor in the raceway counts toward the cross-sectional fill calculation, including equipment grounding conductors and neutrals. Grounding conductors do not count as current-carrying conductors for the separate NEC 310.15(C)(1) derating calculation, but they still occupy space.

4" EMT Conduit Fill Chart

14 AWG THHN

608

conductors max

12 AWG THHN

443

conductors max

10 AWG THHN

279

conductors max

Usable area at 40% fill: 5.901 in² · NEC Chapter 9, Tables 1, 4 and 5

About EMT (Electrical Metallic Tubing)

Thin-wall steel tubing, the most common raceway in commercial interiors and exposed residential work. Joined with set-screw or compression couplings, never threaded. Trade size 4" is covered by NEC Article 358, and its internal dimensions come from NEC Chapter 9, Table 4.

4" EMT — Internal Area & Fill Limits

Trade size	4"
Total internal area (100%)	14.753 in²
1 conductor (53%)	7.819 in²
2 conductors (31%)	4.573 in²
Over 2 conductors (40%)	5.901 in²

4" EMT — Max THHN / THWN-2 Conductors

Wire size	Area (in²)	Max conductors
14	0.0097	608
12	0.0133	443
10	0.0211	279
8	0.0366	161
6	0.0507	116
4	0.0824	71
3	0.0973	60
2	0.1158	50
1	0.1562	37
1/0	0.1855	31
2/0	0.2223	26
3/0	0.2679	22
4/0	0.3237	18
250 kcmil	0.3970	14
300 kcmil	0.4608	12
350 kcmil	0.5242	11
400 kcmil	0.5863	10
500 kcmil	0.7073	8

Conductor areas from NEC Chapter 9, Table 5 (THHN, THWN, THWN-2). Counts assume all conductors are the same size and insulation type, which is the condition NEC Annex C tables are built on. Mix sizes or insulations and you must add the individual areas by hand against the fill area above.

4" EMT — Max XHHW / XHHW-2 Conductors

Wire size	Area (in²)	Max conductors
14	0.0139	424
12	0.0181	326
10	0.0243	242
8	0.0437	135
6	0.0590	100
4	0.0814	72
3	0.0962	61
2	0.1146	51
1	0.1534	38
1/0	0.1825	32
2/0	0.2190	26
3/0	0.2642	22
4/0	0.3197	18
250 kcmil	0.3904	15
350 kcmil	0.5153	11
500 kcmil	0.6984	8

XHHW and XHHW-2 have no nylon jacket, so below 4 AWG they are physically larger than THHN and fewer fit. From 4 AWG up they are slightly smaller. Areas from NEC Chapter 9, Table 5.

How the 40% conduit fill rule works

Conduit fill is a pure area calculation. Take the internal area of the raceway from NEC Chapter 9, Table 4, multiply by the allowable percentage from Table 1, then divide by the area of one conductor from Table 5. Round down — you cannot install a fraction of a wire.

Max conductors = floor( conduit area × fill % ÷ conductor area )

For 4" EMT with 12 AWG THHN: floor( 14.753 × 0.40 ÷ 0.0133 ) = 443 conductors

The three percentages in NEC Chapter 9, Table 1 are not arbitrary. A single conductor gets 53% because it can be pulled straight down the middle. Exactly two conductors get only 31% because two circles inside a circle waste the most space. Three or more conductors nest efficiently again, so the limit rises to 40%.

Fill is only half the job. Once you have more than three current-carrying conductors in the same raceway, NEC 310.15(C)(1) also derates their ampacity — 80% for 4–6 conductors, 70% for 7–9, 50% for 10–20. A conduit can be legally filled and still leave your conductors undersized for the load. See NEC Table 310.15 for the full derating factors.

Nipples are the exception: a conduit or tubing length not exceeding 24 inches between boxes or enclosures may be filled to 60% per NEC Chapter 9, Table 1, Note 4 — and no ampacity derating applies to it. For 4" EMT that raises the usable area from 5.901 in² to 8.852 in².