NEC Conduit Fill Reference

Maximum conductor fill per NEC Chapter 9 Tables 1, 4, and 5 for EMT, IMC, RMC, and PVC conduit.

README

Table1 Fill

NEC Chapter 9 Table 1 - Percent of Conduit Cross Section

Number of Conductors	All Conductor Types	Notes
1	53%	Single conductor - highest fill allowed
2	31%	Two conductors - derate for space
Over 2	40%	Three or more conductors

Conduit Areas

NEC Table 4 - Conduit Internal Areas (in^2) and 40%/31%/53% fill

Trade Size	EMT_Total	EMT_40%	EMT_53%	IMC_Total	IMC_40%	IMC_53%	RMC_Total	RMC_40%	RMC_53%	PVC40_Total	PVC40_40%	PVC40_53%
1/2"	0.304	0.122	0.161	0.342	0.137	0.181	0.314	0.126	0.166	0.285	0.114	0.151
3/4"	0.533	0.213	0.282	0.586	0.234	0.311	0.549	0.22	0.291	0.508	0.203	0.269
1"	0.864	0.346	0.458	0.959	0.384	0.508	0.887	0.355	0.47	0.832	0.333	0.441
1-1/4"	1.496	0.598	0.793	1.647	0.659	0.873	1.526	0.61	0.809	1.453	0.581	0.77
1-1/2"	2.036	0.814	1.079	2.225	0.89	1.179	2.071	0.828	1.098	1.986	0.794	1.053
2"	3.356	1.342	1.779	3.63	1.452	1.924	3.408	1.363	1.806	3.291	1.316	1.744
2-1/2"	5.858	2.343	3.105	5.135	2.054	2.722	4.866	1.946	2.579	4.695	1.878	2.488
3"	8.846	3.538	4.688	7.922	3.169	4.199	7.499	3	3.974	7.268	2.907	3.852
3-1/2"	11.545	4.618	6.119	10.584	4.234	5.61	10.01	4.004	5.305	9.737	3.895	5.161
4"	14.753	5.901	7.819	13.631	5.452	7.224	12.882	5.153	6.827	12.554	5.022	6.654
5"							20.212	8.085	10.712	19.761	7.904	10.473
6"							29.158	11.663	15.454	28.567	11.427	15.141
Source: NEC 2023 Table 4, Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), Electrical Metallic Tubing (EMT), and PVC Schedule 40

Conductor Areas

NEC Table 5 - THHN/THWN/THWN-2 Conductor Areas (in^2)

Size (AWG/kcmil)	Approx Area (in^2)	Notes
14 AWG	0.0097
12 AWG	0.0133
10 AWG	0.0211
8 AWG	0.0366
6 AWG	0.0507
4 AWG	0.0824
3 AWG	0.0973
2 AWG	0.1158
1 AWG	0.1562
1/0	0.1855
2/0	0.2223
3/0	0.2679
4/0	0.3237
250 kcmil	0.397
300 kcmil	0.4608
350 kcmil	0.5242
400 kcmil	0.5863
500 kcmil	0.7073
600 kcmil	0.8676
750 kcmil	1.0496
1000 kcmil	1.3561

AnnexC EMT THHN

NEC Annex C, Table C.1 - Max THHN/THWN in EMT

AWG/kcmil	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	12	22	35	61	84	138	241	364	476	608
12 AWG	9	16	26	45	61	101	176	266	347	443
10 AWG	5	10	16	28	38	63	111	167	219	279
8 AWG	3	6	9	16	22	36	64	96	126	161
6 AWG	2	4	6	11	15	26	46	69	91	116
4 AWG	1	2	4	7	9	16	28	43	56	71
3 AWG	1	1	3	6	8	13	24	36	47	60
2 AWG	1	1	3	5	7	11	20	30	40	51
1 AWG	0	1	1	3	5	8	15	22	29	37
1/0	0	1	1	3	4	7	12	19	25	32
2/0	0	1	1	2	3	6	10	16	20	26
3/0	0	1	1	1	3	5	8	13	17	22
4/0	0	0	1	1	2	4	7	11	14	18
250 kcmil	0	0	0	1	1	3	6	9	11	14
300 kcmil	0	0	0	1	1	3	5	7	10	12
350 kcmil	0	0	0	1	1	2	4	6	8	11
400 kcmil	0	0	0	1	1	2	4	6	7	9
500 kcmil	0	0	0	0	1	1	3	4	6	8
600 kcmil	0	0	0	0	1	1	2	3	5	6
750 kcmil	0	0	0	0	0	1	2	3	4	5
1000 kcmil	0	0	0	0	0	1	1	2	3	4
Source: NEC 2023 Annex C Table C.1

AnnexC RMC THHN

NEC Annex C, Table C.8 - Max THHN/THWN in RMC

AWG/kcmil	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	62	85	140	200	309	412	531	833	1202
12 AWG	9	16	26	45	62	102	146	225	301	387	608	877
10 AWG	6	10	17	28	39	64	92	141	189	244	383	552
8 AWG	3	6	9	16	22	37	53	81	109	140	221	318
6 AWG	2	4	6	12	16	26	38	58	78	101	159	230
4 AWG	1	2	4	7	10	16	24	36	48	62	98	141
3 AWG	1	2	3	6	8	14	20	30	41	53	83	120
2 AWG	1	1	3	5	7	11	17	26	34	44	70	101
1 AWG	1	1	1	4	5	8	12	19	25	33	51	74
1/0	0	1	1	3	4	7	10	16	21	28	43	63
2/0	0	1	1	3	4	6	9	13	18	23	36	52
3/0	0	1	1	2	3	5	7	11	15	19	30	43
4/0	0	1	1	1	2	4	6	9	12	16	25	36
250 kcmil	0	0	1	1	1	3	5	7	10	13	20	29
300 kcmil	0	0	1	1	1	3	4	6	8	11	17	25
350 kcmil	0	0	0	1	1	2	4	6	7	10	15	22
400 kcmil	0	0	0	1	1	2	3	5	7	9	14	20
500 kcmil	0	0	0	1	1	1	3	4	6	7	11	16
600 kcmil	0	0	0	0	1	1	2	3	4	6	9	13
750 kcmil	0	0	0	0	1	1	1	3	4	5	8	11
1000 kcmil	0	0	0	0	0	1	1	2	3	4	6	9
Source: NEC 2023 Annex C Table C.8

Calc Example

Conduit Fill Calculation Example

Scenario	6 conductors #4 AWG THHN in EMT conduit
Conductor area (Table 5)	0.0824 in^2 each
Total conductor area	6 x 0.0824 = 0.4944 in^2
Required conduit fill %	40% (>2 conductors)
Min conduit internal area	0.4944 / 0.40 = 1.236 in^2
Select EMT size (Table 4)	1-1/4" EMT has 40% fill = 0.598 in^2 (insufficient)
	1-1/2" EMT has 40% fill = 0.814 in^2 (sufficient)
Verify via Annex C.1	1-1/2" EMT max #4 THHN = 9 (>=6, OK)
Result	Use 1-1/2" EMT conduit

Source: NEC_Conduit_Fill_Reference_v1.xlsx

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