📋NEC conduit fill chart

By the AmpSizer editorial desk

✓ Tested & verified Updated: Aug 10, 2026 How we calculate this

The limit is 53% of the raceway’s internal area for one conductor, 31% for exactly two, and 40% for three or more — NEC Chapter 9, Table 1. A nipple no longer than 24 inches gets 60%.

Two conductors getting the tightest allowance looks like a misprint and is not: two round conductors of similar diameter can wedge against each other going round a bend in a way three cannot.

In practice the numbers are generous. Half-inch EMT takes nine 12 AWG THHN conductors at 40%, which is more than anybody pulls — the friction of four bends and the derating for more than three current-carrying conductors both bite long before the area does.

EMT — thin-wall steel

The most common raceway in commercial interiors, and the reference everyone quotes.

EMT (thin-wall steel) — how many THHN or THWN-2 conductors of one size fit at the 40 % fill limit. Computed from NEC Chapter 9, Table 4 and Table 5.
Conductor	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	12	21	35	61	83	138	241	364	476	608
12 AWG	9	16	25	44	61	100	176	266	347	443
10 AWG	5	10	16	28	38	63	111	167	218	279
8 AWG	3	5	9	16	22	36	64	96	126	161
6 AWG	2	4	6	11	16	26	46	69	91	116
4 AWG	1	2	4	7	9	16	28	42	56	71
3 AWG	1	2	3	6	8	13	24	36	47	60
2 AWG	1	1	2	5	7	11	20	30	39	50
1 AWG	—	1	2	3	5	8	15	22	29	37
1/0 AWG	—	1	1	3	4	7	12	19	24	31
2/0 AWG	—	—	1	2	3	6	10	15	20	26
3/0 AWG	—	—	1	2	3	5	8	13	17	22
4/0 AWG	—	—	1	1	2	4	7	10	14	18
250 kcmil	—	—	—	1	2	3	5	8	11	14
300 kcmil	—	—	—	1	1	2	5	7	10	12
350 kcmil	—	—	—	1	1	2	4	6	8	11
400 kcmil	—	—	—	1	1	2	3	6	7	10
500 kcmil	—	—	—	—	1	1	3	5	6	8
600 kcmil	—	—	—	—	—	1	2	4	5	6
700 kcmil	—	—	—	—	—	1	2	3	4	5
750 kcmil	—	—	—	—	—	1	2	3	4	5

PVC Schedule 40

Underground, outdoors, and in slabs. Slightly less room than EMT of the same trade size.

PVC Schedule 40 — how many THHN or THWN-2 conductors of one size fit at the 40 % fill limit. Computed from NEC Chapter 9, Table 4 and Table 5.
Conductor	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	11	20	34	59	81	135	193	299	401	517
12 AWG	8	15	25	43	59	98	141	218	292	377
10 AWG	5	9	15	27	37	62	89	137	184	237
8 AWG	3	5	9	15	21	35	51	79	106	137
6 AWG	2	4	6	11	15	25	37	57	76	99
4 AWG	1	2	4	7	9	15	22	35	47	60
3 AWG	1	2	3	5	8	13	19	29	40	51
2 AWG	—	1	2	5	6	11	16	25	33	43
1 AWG	—	1	2	3	5	8	12	18	24	32
1/0 AWG	—	1	1	3	4	7	10	15	20	27
2/0 AWG	—	—	1	2	3	5	8	13	17	22
3/0 AWG	—	—	1	2	2	4	7	10	14	18
4/0 AWG	—	—	1	1	2	4	5	8	12	15
250 kcmil	—	—	—	1	2	3	4	7	9	12
300 kcmil	—	—	—	1	1	2	4	6	8	10
350 kcmil	—	—	—	1	1	2	3	5	7	9
400 kcmil	—	—	—	—	1	2	3	4	6	8
500 kcmil	—	—	—	—	1	1	2	4	5	7
600 kcmil	—	—	—	—	—	1	2	3	4	5
700 kcmil	—	—	—	—	—	1	1	2	3	5
750 kcmil	—	—	—	—	—	1	1	2	3	4

PVC Schedule 80

Where physical protection is needed — exposed risers, bollards. The thicker wall costs real capacity.

PVC Schedule 80 — how many THHN or THWN-2 conductors of one size fit at the 40 % fill limit. Computed from NEC Chapter 9, Table 4 and Table 5.
Conductor	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	8	16	28	51	70	118	169	265	358	464
12 AWG	6	12	20	37	51	86	123	193	261	338
10 AWG	4	7	13	23	32	54	78	122	164	213
8 AWG	2	4	7	13	18	31	45	70	94	123
6 AWG	1	3	5	9	13	22	32	50	68	88
4 AWG	1	1	3	6	8	13	19	31	42	54
3 AWG	—	1	2	5	7	11	16	26	35	46
2 AWG	—	1	2	4	5	9	14	22	30	38
1 AWG	—	1	1	3	4	7	10	16	22	28
1/0 AWG	—	—	1	2	3	6	8	13	18	24
2/0 AWG	—	—	1	2	3	5	7	11	15	20
3/0 AWG	—	—	1	1	2	4	6	9	12	16
4/0 AWG	—	—	—	1	2	3	5	7	10	13
250 kcmil	—	—	—	1	1	2	4	6	8	11
300 kcmil	—	—	—	1	1	2	3	5	7	9
350 kcmil	—	—	—	—	1	2	3	4	6	8
400 kcmil	—	—	—	—	1	1	2	4	5	7
500 kcmil	—	—	—	—	—	1	2	3	4	6
600 kcmil	—	—	—	—	—	1	1	2	4	5
700 kcmil	—	—	—	—	—	1	1	2	3	4
750 kcmil	—	—	—	—	—	1	1	2	3	4

Rigid metal conduit

RMC (rigid metal) — how many THHN or THWN-2 conductors of one size fit at the 40 % fill limit. Computed from NEC Chapter 9, Table 4 and Table 5.
Conductor	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	12	22	36	62	85	140	200	309	412	531
12 AWG	9	16	26	45	62	102	146	225	301	387
10 AWG	5	10	16	28	39	64	92	142	189	244
8 AWG	3	6	9	16	22	37	53	81	109	140
6 AWG	2	4	6	12	16	26	38	59	78	101
4 AWG	1	2	4	7	10	16	23	36	48	62
3 AWG	1	2	3	6	8	14	20	30	41	52
2 AWG	1	1	3	5	7	11	16	25	34	44
1 AWG	—	1	2	3	5	8	12	19	25	32
1/0 AWG	—	1	1	3	4	7	10	16	21	27
2/0 AWG	—	—	1	2	3	6	8	13	18	23
3/0 AWG	—	—	1	2	3	5	7	11	14	19
4/0 AWG	—	—	1	1	2	4	6	9	12	15
250 kcmil	—	—	—	1	2	3	4	7	10	12
300 kcmil	—	—	—	1	1	2	4	6	8	11
350 kcmil	—	—	—	1	1	2	3	5	7	9
400 kcmil	—	—	—	1	1	2	3	5	6	8
500 kcmil	—	—	—	—	1	1	2	4	5	7
600 kcmil	—	—	—	—	—	1	2	3	4	5
700 kcmil	—	—	—	—	—	1	1	3	4	5
750 kcmil	—	—	—	—	—	1	1	2	3	4

Flexible metal conduit

Short connections to motors and fixtures, where movement or vibration rules out solid pipe.

FMC (flexible metal, greenfield) — how many THHN or THWN-2 conductors of one size fit at the 40 % fill limit. Computed from NEC Chapter 9, Table 4 and Table 5.
Conductor	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	13	21	33	52	76	134	202	291	396	518
12 AWG	9	16	24	38	55	98	147	212	289	377
10 AWG	6	10	15	24	35	61	93	134	182	238
8 AWG	3	5	8	13	20	35	53	77	105	137
6 AWG	2	4	6	10	14	25	38	55	75	99
4 AWG	1	2	3	6	9	15	23	34	46	61
3 AWG	1	2	3	5	7	13	20	29	39	51
2 AWG	1	1	2	4	6	11	16	24	33	43
1 AWG	—	1	2	3	4	8	12	18	24	32
1/0 AWG	—	1	1	2	4	7	10	15	20	27
2/0 AWG	—	—	1	2	3	5	8	12	17	22
3/0 AWG	—	—	1	1	2	4	7	10	14	18
4/0 AWG	—	—	1	1	2	4	6	8	11	15
250 kcmil	—	—	—	1	1	3	4	7	9	12
300 kcmil	—	—	—	1	1	2	4	6	8	10
350 kcmil	—	—	—	—	1	2	3	5	7	9
400 kcmil	—	—	—	—	1	2	3	4	6	8
500 kcmil	—	—	—	—	1	1	2	3	5	7
600 kcmil	—	—	—	—	—	1	2	3	4	5
700 kcmil	—	—	—	—	—	1	1	2	3	5
750 kcmil	—	—	—	—	—	1	1	2	3	4

Reading these charts properly

They assume one conductor size throughout. A mixed pull needs the area arithmetic, which the conduit fill calculator does with two sizes at once.

They are area limits, not pulling limits. Total bends between pull points are capped at 360 degrees, and friction climbs much faster than fill percentage. A 38% pull through four bends is harder work than 40% through one.

They say nothing about ampacity. Once more than three current-carrying conductors share the raceway, Table 310.15(C)(1) reduces what every one of them can carry: 80% at four to six, 70% at seven to nine, 50% at ten to twenty. Filling a pipe to 40% with current-carrying conductors usually removes the reason you wanted to.

XHHW-2 is not THHN. In small sizes XHHW-2 is slightly fatter and in large sizes slightly slimmer, so it can change a borderline answer in either direction. Switch the insulation in the calculator rather than assuming.

Frequently asked questions

How many wires can I put in 3/4 inch conduit?

Sixteen 12 AWG THHN or ten 10 AWG at the 40% limit in three-quarter inch EMT. For 8 AWG it is five, for 6 AWG four, and for 4 AWG two. Those are area limits and not practical ones: pulling sixteen conductors through a run with two bends is unpleasant, and all sixteen would be derated to 50% of their ampacity.

Does the ground count in conduit fill?

Yes. Fill is about physical space, so every conductor in the raceway counts — grounds, neutrals, travellers, spare pull strings if they were conductors. Derating is the opposite: the equipment grounding conductor never counts there, and the neutral of a balanced multiwire circuit does not either. The two rules count different things because they are measuring different problems.

Is PVC the same as EMT for fill?

Close but not identical. PVC Schedule 40 has a slightly smaller internal area than EMT of the same trade size, and Schedule 80 is noticeably smaller because the wall is thicker. A pull that just fits half-inch EMT can be over the line in half-inch Schedule 80, which is the trap when a plan changes from indoor to underground.

What is the 60 percent nipple rule?

A raceway not exceeding 24 inches in length between two enclosures may be filled to 60%, per Chapter 9, Note 4. The reasoning is that nothing is really being pulled any distance and heat escapes at both ends. It is genuinely useful between a meter and a panel, and it does not extend to a short piece of a long run.

Can I mix conductor sizes in one conduit?

Yes, and it is normal — a feeder with a smaller neutral or ground. The arithmetic is the sum of each conductor’s own area from Chapter 9, Table 5 against the raceway’s area from Table 4. The published charts assume one size throughout, which is why a mixed pull needs a calculation rather than a lookup.

How we calculate this

Every chart on this page is computed at build time from NEC Chapter 9: internal raceway areas from Table 4, insulated conductor cross-sections from Table 5, and permitted fill percentages from Table 1 — 53% for one conductor, 31% for two, 40% for more than two, and 60% for a nipple not over 24 in under Note 4. The count shown is the largest whole number of conductors of that size whose combined area does not exceed 40% of the raceway’s internal area. Where conductor sizes are mixed, the same area arithmetic applies per Note 6 and a published chart cannot be used directly.

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