Flexible Metal (FMC) Conduit Fill Chart

Flexible Metal Conduit (FMC) — NEC Article 348. Spiral-wound interlocked steel or aluminum “Greenfield”. Used for short whips to motors, fixtures and equipment that vibrates or needs to move.

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

Flexible Metal Conduit fill calculator

Conduit type

Trade size

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

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Flexible Metal Conduit sizes

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

Flexible 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 Flexible Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	3/8"	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	4	13	22	33	52	76	135	202	291	396	518
12 AWG	3	9	16	24	38	56	98	147	212	289	378
10 AWG	1	6	10	15	24	35	62	93	134	182	238
8 AWG	1	3	6	9	14	20	35	53	77	105	137
6 AWG	1	1	4	6	10	14	25	38	55	76	99
4 AWG	—	1	2	4	6	9	16	24	34	46	61
3 AWG	—	1	1	3	5	7	13	20	29	39	51
2 AWG	—	1	1	3	4	6	11	17	24	33	43
1 AWG	—	1	1	1	3	4	8	12	18	24	32
1/0 AWG	—	—	1	1	2	4	7	10	15	20	27
2/0 AWG	—	—	1	1	1	3	6	9	12	17	22
3/0 AWG	—	—	1	1	1	2	5	7	10	14	18
4/0 AWG	—	—	—	1	1	1	4	6	8	12	15
250 kcmil	—	—	—	1	1	1	3	5	7	9	12
300 kcmil	—	—	—	—	1	1	3	4	6	8	11
350 kcmil	—	—	—	—	1	1	1	3	5	7	9
400 kcmil	—	—	—	—	1	1	1	3	5	6	8
500 kcmil	—	—	—	—	—	1	1	2	4	5	7
600 kcmil	—	—	—	—	—	1	1	1	3	4	5
700 kcmil	—	—	—	—	—	—	1	1	3	4	5
750 kcmil	—	—	—	—	—	—	1	1	2	3	4
800 kcmil	—	—	—	—	—	—	1	1	1	3	4
900 kcmil	—	—	—	—	—	—	1	1	1	3	4
1000 kcmil	—	—	—	—	—	—	1	1	1	3	3

Flexible 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 Flexible Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	3/8"	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	3	9	15	23	36	53	94	141	203	277	361
12 AWG	1	7	11	18	28	41	72	108	156	212	277
10 AWG	1	5	8	13	21	30	54	81	116	158	207
8 AWG	1	3	5	7	11	17	30	45	64	88	115
6 AWG	1	1	3	5	8	12	22	33	48	65	85
4 AWG	—	1	2	4	6	9	16	24	34	47	61
3 AWG	—	1	1	3	5	7	13	20	29	40	52
2 AWG	—	1	1	3	4	6	11	17	24	33	44
1 AWG	—	1	1	1	3	5	8	13	18	25	32
1/0 AWG	—	—	1	1	2	4	7	10	15	21	27
2/0 AWG	—	—	1	1	1	3	6	9	13	17	23
3/0 AWG	—	—	1	1	1	3	5	7	10	14	19
4/0 AWG	—	—	—	1	1	1	4	6	9	12	15
250 kcmil	—	—	—	1	1	1	3	5	7	10	13
300 kcmil	—	—	—	—	1	1	3	4	6	8	11
350 kcmil	—	—	—	—	1	1	1	4	5	7	9
400 kcmil	—	—	—	—	1	1	1	3	5	6	8
500 kcmil	—	—	—	—	—	1	1	3	4	5	7
600 kcmil	—	—	—	—	—	1	1	1	3	4	5
700 kcmil	—	—	—	—	—	—	1	1	3	4	5
750 kcmil	—	—	—	—	—	—	1	1	2	3	4
800 kcmil	—	—	—	—	—	—	1	1	1	3	4
900 kcmil	—	—	—	—	—	—	1	1	1	3	4
1000 kcmil	—	—	—	—	—	—	1	1	1	3	3

Flexible 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 Flexible Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	3/8"	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	3	9	15	23	36	53	94	141	203	277	361
12 AWG	1	7	11	18	28	41	72	108	156	212	277
10 AWG	1	5	8	13	21	30	54	81	116	158	207
8 AWG	1	3	5	7	11	17	30	45	64	88	115
6 AWG	—	1	3	4	7	10	18	27	39	53	69
4 AWG	—	1	1	3	5	7	13	20	29	39	51
3 AWG	—	1	1	3	4	6	11	17	25	34	44
2 AWG	—	1	1	1	4	5	10	14	21	29	37
1 AWG	—	—	1	1	2	4	7	10	15	20	26
1/0 AWG	—	—	1	1	1	3	6	9	12	17	22
2/0 AWG	—	—	1	1	1	3	5	7	10	14	19
3/0 AWG	—	—	—	1	1	1	4	6	9	12	16
4/0 AWG	—	—	—	1	1	1	3	5	7	10	13
250 kcmil	—	—	—	—	1	1	3	4	6	8	11
300 kcmil	—	—	—	—	1	1	1	3	5	7	9
350 kcmil	—	—	—	—	1	1	1	3	4	6	8
400 kcmil	—	—	—	—	1	1	1	3	4	6	7
500 kcmil	—	—	—	—	—	1	1	1	3	5	6
600 kcmil	—	—	—	—	—	1	1	1	3	4	5
700 kcmil	—	—	—	—	—	—	1	1	1	3	4
750 kcmil	—	—	—	—	—	—	1	1	1	3	4
800 kcmil	—	—	—	—	—	—	1	1	1	3	4
900 kcmil	—	—	—	—	—	—	1	1	1	3	3
1000 kcmil	—	—	—	—	—	—	1	1	1	2	3

Flexible 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 Flexible Metal Conduit — 40% fill (53% for one wire, 31% for two)
Wire size	3/8"	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	1	4	7	11	17	25	44	67	96	131	171
12 AWG	1	3	6	9	14	21	37	55	80	109	142
10 AWG	1	3	5	7	11	17	30	45	64	88	115
8 AWG	—	1	1	4	6	9	15	23	34	46	60
6 AWG	—	1	1	3	5	7	12	19	27	37	48
4 AWG	—	1	1	1	4	5	10	14	21	29	37
3 AWG	—	1	1	1	3	5	8	13	18	25	33
2 AWG	—	—	1	1	3	4	7	11	16	22	28
1 AWG	—	—	1	1	1	2	5	7	10	14	19
1/0 AWG	—	—	—	1	1	1	4	6	9	12	16
2/0 AWG	—	—	—	1	1	1	3	5	8	11	14
3/0 AWG	—	—	—	1	1	1	3	5	7	9	12
4/0 AWG	—	—	—	—	1	1	2	4	6	8	10
250 kcmil	—	—	—	—	1	1	1	3	4	6	8
300 kcmil	—	—	—	—	—	1	1	2	4	5	7
350 kcmil	—	—	—	—	—	1	1	1	3	5	6
400 kcmil	—	—	—	—	—	1	1	1	3	4	6
500 kcmil	—	—	—	—	—	—	1	1	3	4	5
600 kcmil	—	—	—	—	—	—	1	1	1	3	4
700 kcmil	—	—	—	—	—	—	1	1	1	3	3
750 kcmil	—	—	—	—	—	—	1	1	1	2	3
800 kcmil	—	—	—	—	—	—	1	1	1	1	3
900 kcmil	—	—	—	—	—	—	1	1	1	1	3
1000 kcmil	—	—	—	—	—	—	—	1	1	1	3

Flexible Metal Conduit internal diameter and area

Flexible 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%
3/8"	12	0.384	0.116	0.061	0.036	0.046	0.070
1/2"	16	0.635	0.317	0.168	0.098	0.127	0.190
3/4"	21	0.824	0.533	0.282	0.165	0.213	0.320
1"	27	1.020	0.817	0.433	0.253	0.327	0.490
1-1/4"	35	1.275	1.277	0.677	0.396	0.511	0.766
1-1/2"	41	1.538	1.858	0.985	0.576	0.743	1.115
2"	53	2.040	3.269	1.733	1.013	1.308	1.961
2-1/2"	63	2.500	4.909	2.602	1.522	1.964	2.945
3"	78	3.000	7.069	3.747	2.191	2.828	4.241
3-1/2"	91	3.500	9.621	5.099	2.983	3.848	5.773
4"	103	4.000	12.566	6.660	3.895	5.026	7.540

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 Flexible Metal Conduit?

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

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

0.824 inches, giving a total internal area of 0.533 in² and 0.213 in² of usable area at 40% fill.

What is the largest wire that fits in 4-inch Flexible Metal Conduit?

4-inch Flexible Metal Conduit holds 7 conductors of 500 kcmil THHN or 3 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.