4-inch Rigid Metal (RMC) Conduit Fill

Wire capacity of trade size 4 (metric designator 103) Rigid Metal Conduit (RMC), for THHN, XHHW, THW and RHW conductors from 14 AWG to 1000 kcmil.

4-inch Rigid Metal Conduit holds 62 × #4, 44 × #2, 27 × 1/0 AWG or 16 × 4/0 AWG THHN conductors at 40% fill. Internal area: 12.882 in²; usable at 40%: 5.153 in².

Internal diameter

4.050 in · 102.9 mm

Total area

12.882 in² · 8311 mm²

40% fill (3+ wires)

5.153 in²

31% / 53% (2 / 1 wire)

3.993 / 6.827 in²

Maximum conductors in 4-inch Rigid Metal Conduit
Wire size	THHN	XHHW	THW	RHW	THHN in a nipple (60%)	THHN area (in²)
14 AWG	531	370	370	176	797	0.0097
12 AWG	387	284	284	146	581	0.0133
10 AWG	244	212	212	118	366	0.0211
8 AWG	140	118	118	61	211	0.0366
6 AWG	101	87	71	49	152	0.0507
4 AWG	62	63	53	38	94	0.0824
3 AWG	53	53	45	34	79	0.0973
2 AWG	44	45	38	29	66	0.1158
1 AWG	33	33	27	19	49	0.1562
1/0 AWG	27	28	23	17	41	0.1855
2/0 AWG	23	23	19	14	34	0.2223
3/0 AWG	19	19	16	12	29	0.2679
4/0 AWG	16	16	14	11	24	0.3237
250 kcmil	13	13	11	8	19	0.3970
300 kcmil	11	11	9	7	16	0.4608
350 kcmil	10	10	8	6	14	0.5242
400 kcmil	8	9	7	6	13	0.5863
500 kcmil	7	7	6	5	11	0.7073
600 kcmil	6	6	5	4	9	0.8676
700 kcmil	5	5	4	3	8	0.9887
750 kcmil	5	5	4	3	7	1.0496
800 kcmil	4	4	4	3	7	1.1085
900 kcmil	4	4	3	3	6	1.2311
1000 kcmil	4	4	3	3	5	1.3478

Mixed wire sizes? Calculate it

Conduit type

Trade size

Run length Nipple, 24 in. or shorter (60%)

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4-inch conduit: Rigid Metal Conduit vs other types

Trade size is nominal. The real inside diameter, and so the wire count, changes with the wall thickness of each raceway type.

4-inch trade size across conduit types
Conduit type	ID (in)	Area (in²)	40% (in²)	#12 THHN	#10 THHN	#6 THHN
EMT	4.334	14.753	5.901	443	279	116
PVC Schedule 40	3.998	12.554	5.022	377	238	99
PVC Schedule 80	3.786	11.258	4.503	338	213	89
Rigid Metal Conduit	4.050	12.882	5.153	387	244	101
IMC	4.166	13.631	5.452	410	258	107
Flexible Metal Conduit	4.000	12.566	5.026	378	238	99
Liquidtight Flexible Metal Conduit	4.020	12.692	5.077	381	240	100

Other Rigid Metal Conduit sizes

Frequently asked questions

How many #12 wires fit in 4-inch Rigid Metal Conduit?

387 conductors of 12 AWG THHN/THWN-2 at the 40% fill limit. With thicker THW or XHHW insulation the count is 284.

What is the inside diameter and area of 4-inch Rigid Metal Conduit?

The internal diameter is 4.050 in. (102.9 mm) and the total cross-sectional area is 12.882 in². The usable area is 5.153 in² at 40% fill, 3.993 in² for two wires and 6.827 in² for one.

What is the largest wire I can pull three of in 4-inch Rigid Metal Conduit?

1000 kcmil THHN: 4 conductors fit at 40% fill. That is three current-carrying conductors with no ground; add the ground’s area and check again with the calculator if you need one.

Can I really load it with that many conductors?

For space, yes. But 387 current-carrying conductors in one raceway means heavy ampacity derating — 10 to 20 conductors are adjusted to 50% of their table ampacity. Fill tells you what fits; derating tells you what it can carry.

NECTables.com is an independent reference and is not affiliated with, endorsed by, or a substitute for the National Fire Protection Association (NFPA). NEC® and National Electrical Code® are registered trademarks of the NFPA. Values shown are commonly published engineering data and independent calculations based on the methods of NFPA 70; they are not a reproduction of the Code. Always confirm against the edition adopted in your jurisdiction, including local amendments, and consult a licensed electrician or engineer before doing electrical work.