IMC Conduit Fill Chart

Intermediate Metal Conduit — NEC Article 342. Threaded steel conduit with a thinner wall than rigid. Permitted everywhere RMC is, weighs about a third less, and has the largest interior of the three steel raceways.

1/2-inch IMC holds 10 #12 THHN conductors; 3/4-inch holds 17. Counts assume 40% fill with all conductors the same size.

IMC fill calculator

Conduit type

Trade size

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

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IMC sizes

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

IMC 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 IMC — 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"
14 AWG	14	24	39	68	91	149	211	326	436	562
12 AWG	10	17	29	49	67	109	154	238	318	410
10 AWG	6	11	18	31	42	69	97	150	200	258
8 AWG	3	6	10	18	24	39	56	86	115	149
6 AWG	2	4	7	13	17	28	40	62	83	107
4 AWG	1	3	4	8	11	17	25	38	51	66
3 AWG	1	1	4	6	9	15	21	32	43	56
2 AWG	1	1	3	5	7	12	17	27	36	47
1 AWG	1	1	1	4	5	9	13	20	27	35
1/0 AWG	—	1	1	3	4	8	11	17	23	29
2/0 AWG	—	1	1	3	4	6	9	14	19	24
3/0 AWG	—	1	1	1	3	5	7	12	16	20
4/0 AWG	—	—	1	1	2	4	6	9	13	17
250 kcmil	—	—	1	1	1	3	5	8	10	13
300 kcmil	—	—	1	1	1	3	4	7	9	12
350 kcmil	—	—	—	1	1	2	4	6	8	10
400 kcmil	—	—	—	1	1	1	3	5	7	9
500 kcmil	—	—	—	1	1	1	3	4	6	7
600 kcmil	—	—	—	1	1	1	1	3	5	6
700 kcmil	—	—	—	—	1	1	1	3	4	5
750 kcmil	—	—	—	—	1	1	1	3	4	5
800 kcmil	—	—	—	—	1	1	1	3	4	5
900 kcmil	—	—	—	—	—	1	1	1	3	4
1000 kcmil	—	—	—	—	—	1	1	1	3	4

IMC 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 IMC — 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"
14 AWG	10	17	27	47	64	104	147	228	304	392
12 AWG	7	13	21	36	49	80	113	175	234	301
10 AWG	5	9	15	27	36	59	84	130	174	224
8 AWG	3	5	8	15	20	33	47	72	97	124
6 AWG	1	4	6	11	15	24	35	53	71	92
4 AWG	1	3	4	8	11	18	25	39	52	67
3 AWG	1	1	4	7	9	15	21	33	44	56
2 AWG	1	1	3	5	7	12	18	27	37	47
1 AWG	1	1	1	4	6	9	13	20	27	35
1/0 AWG	—	1	1	3	5	8	11	17	23	30
2/0 AWG	—	1	1	3	4	6	9	14	19	25
3/0 AWG	—	1	1	1	3	5	7	12	16	20
4/0 AWG	—	—	1	1	2	4	6	10	13	17
250 kcmil	—	—	1	1	1	3	5	8	11	14
300 kcmil	—	—	1	1	1	3	4	7	9	12
350 kcmil	—	—	—	1	1	3	4	6	8	10
400 kcmil	—	—	—	1	1	1	3	5	7	9
500 kcmil	—	—	—	1	1	1	3	4	6	8
600 kcmil	—	—	—	1	1	1	1	3	5	6
700 kcmil	—	—	—	—	1	1	1	3	4	5
750 kcmil	—	—	—	—	1	1	1	3	4	5
800 kcmil	—	—	—	—	1	1	1	3	4	5
900 kcmil	—	—	—	—	—	1	1	1	3	4
1000 kcmil	—	—	—	—	—	1	1	1	3	4

IMC 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 IMC — 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"
14 AWG	10	17	27	47	64	104	147	228	304	392
12 AWG	7	13	21	36	49	80	113	175	234	301
10 AWG	5	9	15	27	36	59	84	130	174	224
8 AWG	3	5	8	15	20	33	47	72	97	124
6 AWG	1	3	5	9	12	20	28	43	58	75
4 AWG	1	1	4	6	9	15	21	32	43	56
3 AWG	1	1	3	6	8	13	18	28	37	48
2 AWG	1	1	3	5	6	11	15	23	31	41
1 AWG	—	1	1	3	4	7	11	16	22	28
1/0 AWG	—	1	1	3	4	6	9	14	19	24
2/0 AWG	—	1	1	1	3	5	8	12	16	20
3/0 AWG	—	—	1	1	3	4	6	10	13	17
4/0 AWG	—	—	1	1	1	4	5	8	11	14
250 kcmil	—	—	1	1	1	3	4	7	9	12
300 kcmil	—	—	—	1	1	2	4	6	8	10
350 kcmil	—	—	—	1	1	1	3	5	7	9
400 kcmil	—	—	—	1	1	1	3	4	6	8
500 kcmil	—	—	—	1	1	1	2	4	5	7
600 kcmil	—	—	—	—	1	1	1	3	4	5
700 kcmil	—	—	—	—	1	1	1	3	4	5
750 kcmil	—	—	—	—	1	1	1	2	3	4
800 kcmil	—	—	—	—	—	1	1	2	3	4
900 kcmil	—	—	—	—	—	1	1	1	3	4
1000 kcmil	—	—	—	—	—	1	1	1	3	3

IMC 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 IMC — 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"
14 AWG	4	8	13	22	30	49	70	108	144	186
12 AWG	4	6	11	18	25	41	58	89	120	154
10 AWG	3	5	8	15	20	33	47	72	97	124
8 AWG	1	3	4	8	10	17	24	38	50	65
6 AWG	1	1	3	6	8	14	19	30	40	52
4 AWG	1	1	3	5	6	11	15	23	31	41
3 AWG	1	1	1	4	6	9	13	21	28	36
2 AWG	1	1	1	3	5	8	11	18	24	31
1 AWG	—	1	1	1	3	5	7	12	16	20
1/0 AWG	—	1	1	1	3	4	6	10	14	18
2/0 AWG	—	—	1	1	1	4	6	9	12	15
3/0 AWG	—	—	1	1	1	3	5	7	10	13
4/0 AWG	—	—	1	1	1	3	4	6	9	11
250 kcmil	—	—	—	1	1	1	3	5	6	8
300 kcmil	—	—	—	1	1	1	3	4	6	7
350 kcmil	—	—	—	1	1	1	2	4	5	7
400 kcmil	—	—	—	1	1	1	1	3	5	6
500 kcmil	—	—	—	—	1	1	1	3	4	5
600 kcmil	—	—	—	—	—	1	1	2	3	4
700 kcmil	—	—	—	—	—	1	1	1	3	4
750 kcmil	—	—	—	—	—	1	1	1	3	4
800 kcmil	—	—	—	—	—	1	1	1	3	3
900 kcmil	—	—	—	—	—	1	1	1	2	3
1000 kcmil	—	—	—	—	—	1	1	1	1	3

IMC internal diameter and area

IMC 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	0.660	0.342	0.181	0.106	0.137	0.205
3/4"	21	0.864	0.586	0.311	0.182	0.234	0.352
1"	27	1.105	0.959	0.508	0.297	0.384	0.575
1-1/4"	35	1.448	1.647	0.873	0.511	0.659	0.988
1-1/2"	41	1.683	2.225	1.179	0.690	0.890	1.335
2"	53	2.150	3.630	1.924	1.125	1.452	2.178
2-1/2"	63	2.557	5.135	2.722	1.592	2.054	3.081
3"	78	3.176	7.922	4.199	2.456	3.169	4.753
3-1/2"	91	3.671	10.584	5.610	3.281	4.234	6.350
4"	103	4.166	13.631	7.224	4.226	5.452	8.179

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 IMC?

10 conductors of 12 AWG THHN/THWN-2, or 7 of the thicker THW. In 3/4-inch IMC the count rises to 17 THHN.

How many #10 wires fit in 1/2-inch IMC?

6 conductors of 10 AWG THHN in 1/2-inch, and 11 in 3/4-inch.

What is the inside diameter of 3/4-inch IMC?

0.864 inches, giving a total internal area of 0.586 in² and 0.234 in² of usable area at 40% fill.

What is the largest wire that fits in 4-inch IMC?

4-inch IMC holds 7 conductors of 500 kcmil THHN or 4 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.