Rigid Metal (RMC) Conduit Fill Chart

Rigid Metal Conduit (RMC) — NEC Article 344. Threaded heavy-wall galvanized steel (or aluminum) conduit. The most protective raceway; used for services, hazardous locations and anywhere subject to severe physical damage.

1/2-inch Rigid Metal Conduit holds 9 #12 THHN conductors; 3/4-inch holds 16. Counts assume 40% fill with all conductors the same size.

Rigid Metal Conduit fill calculator

Conduit type

Trade size

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

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Rigid Metal Conduit sizes

One page per trade size, with counts for every insulation type side by side.

Rigid Metal Conduit fill chart — THHN / THWN-2

Thermoplastic insulation with a nylon jacket. The thinnest common building wire, so it gives the highest conductor counts. Nearly all pulled wire sold in North America is dual-rated THHN/THWN-2.

Maximum THHN conductors in Rigid Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"	5"	6"
14 AWG	13	22	36	63	85	140	200	309	412	531	833	1202
12 AWG	9	16	26	46	62	102	146	225	301	387	608	877
10 AWG	6	10	17	29	39	64	92	142	189	244	383	552
8 AWG	3	6	9	16	22	37	53	82	109	140	221	318
6 AWG	1	4	7	12	16	27	38	59	79	101	159	230
4 AWG	1	2	4	7	10	16	23	36	48	62	98	141
3 AWG	1	1	3	6	8	14	20	31	41	53	83	120
2 AWG	1	1	3	5	7	11	17	26	34	44	70	100
1 AWG	1	1	1	4	5	8	12	19	25	33	51	74
1/0 AWG	—	1	1	3	4	7	10	16	21	27	43	63
2/0 AWG	—	1	1	2	3	6	8	13	18	23	36	52
3/0 AWG	—	1	1	1	3	5	7	11	15	19	30	43
4/0 AWG	—	—	1	1	1	4	6	9	12	16	25	36
250 kcmil	—	—	1	1	1	3	5	7	10	13	20	29
300 kcmil	—	—	1	1	1	3	4	6	8	11	17	25
350 kcmil	—	—	—	1	1	2	3	5	7	10	15	22
400 kcmil	—	—	—	1	1	1	3	5	7	8	13	20
500 kcmil	—	—	—	1	1	1	2	4	5	7	11	16
600 kcmil	—	—	—	—	1	1	1	3	4	6	9	13
700 kcmil	—	—	—	—	1	1	1	3	4	5	8	11
750 kcmil	—	—	—	—	1	1	1	3	4	5	7	11
800 kcmil	—	—	—	—	—	1	1	2	3	4	7	10
900 kcmil	—	—	—	—	—	1	1	1	3	4	6	9
1000 kcmil	—	—	—	—	—	1	1	1	3	4	6	8

Rigid Metal Conduit fill chart — XHHW / XHHW-2

Cross-linked polyethylene (XLPE) insulation, no nylon jacket. Standard for aluminum feeders and common for larger copper feeders. Slightly fatter than THHN in small sizes, slightly thinner above 4 AWG.

Maximum XHHW conductors in Rigid Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"	5"	6"
14 AWG	9	15	25	44	59	98	140	215	288	370	581	839
12 AWG	7	12	19	33	45	75	107	165	221	284	446	644
10 AWG	5	9	14	25	34	56	80	123	164	212	332	480
8 AWG	3	5	8	14	19	31	44	68	91	118	185	267
6 AWG	1	3	6	10	14	23	33	51	68	87	137	197
4 AWG	1	2	4	7	10	16	24	37	49	63	99	143
3 AWG	1	1	3	6	8	14	20	31	41	53	84	121
2 AWG	1	1	3	5	7	12	17	26	35	45	70	101
1 AWG	1	1	1	4	5	9	12	19	26	33	52	76
1/0 AWG	—	1	1	3	4	7	10	16	22	28	44	64
2/0 AWG	—	1	1	2	3	6	9	13	18	23	37	53
3/0 AWG	—	1	1	1	3	5	7	11	15	19	30	44
4/0 AWG	—	—	1	1	2	4	6	9	12	16	25	36
250 kcmil	—	—	1	1	1	3	5	7	10	13	20	30
300 kcmil	—	—	1	1	1	3	4	6	9	11	18	25
350 kcmil	—	—	—	1	1	2	3	6	7	10	15	22
400 kcmil	—	—	—	1	1	1	3	5	7	9	14	20
500 kcmil	—	—	—	1	1	1	2	4	5	7	11	16
600 kcmil	—	—	—	—	1	1	1	3	4	6	9	13
700 kcmil	—	—	—	—	1	1	1	3	4	5	8	11
750 kcmil	—	—	—	—	1	1	1	3	4	5	7	11
800 kcmil	—	—	—	—	—	1	1	2	3	4	7	10
900 kcmil	—	—	—	—	—	1	1	1	3	4	6	9
1000 kcmil	—	—	—	—	—	1	1	1	3	4	6	8

Rigid Metal Conduit fill chart — THW / THHW / TW

Older thick-wall thermoplastic insulation without a nylon jacket. Rarely installed new, but it is what you will find in many existing conduits, and it takes considerably more room than THHN.

Maximum THW conductors in Rigid Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"	5"	6"
14 AWG	9	15	25	44	59	98	140	215	288	370	581	839
12 AWG	7	12	19	33	45	75	107	165	221	284	446	644
10 AWG	5	9	14	25	34	56	80	123	164	212	332	480
8 AWG	3	5	8	14	19	31	44	68	91	118	185	267
6 AWG	1	3	5	8	11	18	27	41	55	71	111	160
4 AWG	1	1	3	6	8	14	20	31	41	53	83	120
3 AWG	1	1	3	5	7	12	17	26	35	45	71	103
2 AWG	1	1	2	4	6	10	14	22	30	38	60	87
1 AWG	—	1	1	3	4	7	10	15	21	27	42	61
1/0 AWG	—	1	1	2	3	6	8	13	18	23	36	52
2/0 AWG	—	1	1	1	3	5	7	11	15	19	31	44
3/0 AWG	—	—	1	1	2	4	6	9	13	16	26	37
4/0 AWG	—	—	1	1	1	3	5	8	10	14	21	31
250 kcmil	—	—	1	1	1	3	4	6	8	11	17	25
300 kcmil	—	—	—	1	1	2	3	5	7	9	15	22
350 kcmil	—	—	—	1	1	1	3	5	6	8	13	19
400 kcmil	—	—	—	1	1	1	3	4	6	7	12	17
500 kcmil	—	—	—	1	1	1	1	3	5	6	10	14
600 kcmil	—	—	—	—	1	1	1	3	4	5	8	12
700 kcmil	—	—	—	—	—	1	1	2	3	4	7	10
750 kcmil	—	—	—	—	—	1	1	1	3	4	7	10
800 kcmil	—	—	—	—	—	1	1	1	3	4	6	9
900 kcmil	—	—	—	—	—	1	1	1	3	3	6	8
1000 kcmil	—	—	—	—	—	1	1	1	2	3	5	8

Rigid Metal Conduit fill chart — RHH / RHW-2

Thermoset rubber-type insulation with an outer covering. The bulkiest of the common types; counts drop to roughly half of THHN in small conduit.

Maximum RHW conductors in Rigid Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"	5"	6"
14 AWG	4	7	12	21	28	46	66	102	136	176	276	398
12 AWG	3	6	10	17	23	38	55	85	113	146	229	330
10 AWG	3	5	8	14	19	31	44	68	91	118	185	267
8 AWG	1	2	4	7	10	16	23	36	48	61	97	139
6 AWG	1	1	3	6	8	13	18	29	38	49	77	112
4 AWG	1	1	2	4	6	10	14	22	30	38	60	87
3 AWG	1	1	1	4	5	9	12	19	26	34	53	76
2 AWG	—	1	1	3	4	7	11	17	23	29	46	66
1 AWG	—	1	1	1	3	5	7	11	15	19	30	44
1/0 AWG	—	—	1	1	2	4	6	10	13	17	26	38
2/0 AWG	—	—	1	1	1	4	5	8	11	14	23	33
3/0 AWG	—	—	1	1	1	3	4	7	10	12	20	28
4/0 AWG	—	—	—	1	1	3	4	6	8	11	17	24
250 kcmil	—	—	—	1	1	1	3	4	6	8	13	18
300 kcmil	—	—	—	1	1	1	2	4	5	7	11	16
350 kcmil	—	—	—	1	1	1	1	4	5	6	10	15
400 kcmil	—	—	—	—	1	1	1	3	4	6	9	13
500 kcmil	—	—	—	—	1	1	1	3	4	5	8	11
600 kcmil	—	—	—	—	—	1	1	1	3	4	6	9
700 kcmil	—	—	—	—	—	1	1	1	3	3	6	8
750 kcmil	—	—	—	—	—	1	1	1	3	3	5	8
800 kcmil	—	—	—	—	—	1	1	1	2	3	5	7
900 kcmil	—	—	—	—	—	1	1	1	1	3	5	7
1000 kcmil	—	—	—	—	—	1	1	1	1	3	4	6

Rigid Metal Conduit internal diameter and area

Rigid Metal Conduit internal dimensions and allowable fill area
Trade size	Metric designator	Internal dia. (in)	Total area (in²)	1 wire — 53%	2 wires — 31%	Over 2 — 40%	Nipple — 60%
1/2"	16	0.632	0.314	0.166	0.097	0.126	0.188
3/4"	21	0.836	0.549	0.291	0.170	0.220	0.329
1"	27	1.063	0.887	0.470	0.275	0.355	0.532
1-1/4"	35	1.394	1.526	0.809	0.473	0.610	0.916
1-1/2"	41	1.624	2.071	1.098	0.642	0.828	1.243
2"	53	2.083	3.408	1.806	1.056	1.363	2.045
2-1/2"	63	2.489	4.866	2.579	1.508	1.946	2.920
3"	78	3.090	7.499	3.974	2.325	3.000	4.499
3-1/2"	91	3.570	10.010	5.305	3.103	4.004	6.006
4"	103	4.050	12.882	6.827	3.993	5.153	7.729
5"	129	5.073	20.212	10.712	6.266	8.085	12.127
6"	155	6.093	29.158	15.454	9.039	11.663	17.495

Fill limits that apply

Allowable conduit fill (Chapter 9, Table 1 and its notes)
Conductors in the raceway	Maximum fill	Why
1	53%	A single conductor cannot jam, so more of the area can be used.
2	31%	Two conductors lie side by side and wedge easily in bends, so the limit is lowest.
3 or more	40%	The everyday limit. Leaves room to pull and for heat to escape.
Nipple ≤ 24 in.	60%	Short sections between boxes or enclosures; derating for conductor count does not apply either.

Frequently asked questions

How many #12 wires can I put in 1/2-inch Rigid Metal Conduit?

9 conductors of 12 AWG THHN/THWN-2, or 7 of the thicker THW. In 3/4-inch Rigid Metal Conduit the count rises to 16 THHN.

How many #10 wires fit in 1/2-inch Rigid Metal Conduit?

6 conductors of 10 AWG THHN in 1/2-inch, and 10 in 3/4-inch.

What is the inside diameter of 3/4-inch Rigid Metal Conduit?

0.836 inches, giving a total internal area of 0.549 in² and 0.220 in² of usable area at 40% fill.

What is the largest wire that fits in 6-inch Rigid Metal Conduit?

6-inch Rigid Metal Conduit holds 16 conductors of 500 kcmil THHN or 8 of 1000 kcmil.

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.