🛠️How many wires fit in a conduit?

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

Conduit fill calculator

Raceway

Insulation

Conductor size

How many of them

Trade size you have

Length of the run

17.5 % full of 40% allowed

Smallest raceway that takes this pull: 1/2" · 4 conductors are 0.053 in²

17.5% of 40% allowed

Area allowed in 1/2": 0.122 in² of 0.304
Each 12 AWG conductor: 0.013 in²
Room left for more of the same size: 5

Count every conductor, grounds included — fill is about space, so nothing is left out.

A sizing aid from the published NEC tables, not a design — have it signed off by a licensed electrician against the code your inspector enforces. Calculations follow the US NEC; outside the US, follow your local electrical code.

Try also

How many wires fit in a conduit?

The AmpSizer conduit fill result for four 12 AWG THHN conductors in half-inch EMT is 17.5% of the raceway — comfortably inside the 40% ceiling, with room for five more of the same size.

The ceilings are in Chapter 9, Table 1, and they are not in the order people expect: 53% for one conductor, 31% for exactly two, 40% for three or more. Two gets the tightest limit because two round conductors can jam against each other going round a bend.

A nipple — a raceway no longer than 24 inches between two enclosures — gets 60%, because nothing is being pulled any distance through it and heat has somewhere to go at both ends.

The chart below is the whole of EMT at the 40% limit, computed from the code tables rather than retyped from one. Every column is a trade size, every row a conductor, and every cell is how many of that conductor the pipe legally takes.

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 and outdoors, PVC is the usual choice, and its internal area is slightly smaller than EMT of the same trade size — so a pull that just fits in EMT can be one conductor over the line in PVC.

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

What to do when it does not fit

Go up one trade size. Almost always the right answer, and at rough-in the cheapest one.

Split the pull. Two smaller raceways instead of one larger is sometimes cheaper in fittings, and it avoids the derating that comes with bundling everything together.

Change insulation. XHHW-2 is slightly larger than THHN in small sizes and slightly smaller in large ones, so it can go either way. It is worth checking rather than assuming.

Add a pull point. If the problem is friction rather than area, a junction box in the middle of the run does more good than a bigger pipe.

Frequently asked questions

How many 12 gauge wires fit in a half inch EMT?

Nine 12 AWG THHN conductors at the 40% limit, which is a number almost nobody needs — the practical limit arrives long before the arithmetic does. Four circuits of two conductors plus grounds is already awkward to pull through two bends, and derating for more than three current-carrying conductors will have cut the ampacity of all of them before you get near nine.

Does the ground wire count toward conduit fill?

Yes. Every conductor in the raceway takes up space, so grounds, neutrals and travellers all count. This is the opposite of derating, where the equipment grounding conductor never counts and a balanced multiwire neutral does not either. Fill is about geometry, derating is about heat, and the two rules count different things on purpose.

Why is 31% the limit for two conductors when three get 40%?

Because of jamming. Two conductors of similar diameter can wedge side by side against the inside of a bend in a way that three cannot, and the lower percentage is the margin that stops it happening. It is the one entry in the table that looks like a misprint and is not.

Is 40% a hard limit or a guideline?

It is a requirement — Chapter 9, Table 1 is code text, not an informational note, and an inspector can reject an overfilled raceway. Practically, it is also the point past which conductors stop pulling: friction rises much faster than fill percentage does, and jacket damage on the way in is a fault you will meet years later.

Do the conductors have to be the same size?

No, and mixed pulls are normal — a feeder plus its neutral plus a smaller ground. The arithmetic is just the sum of each conductor’s own area from Chapter 9, Table 5 against the raceway’s internal area from Table 4. Add a second size in the fields and the total updates.

How we calculate this

Fill is the sum of the conductors’ cross-sectional areas divided by the internal area of the raceway. Conductor areas are NEC Chapter 9, Table 5 for THHN/THWN-2 and XHHW-2; raceway internal areas are Chapter 9, Table 4 for EMT, PVC Schedule 40 and 80, RMC, IMC, ENT and FMC. The permitted percentages are Chapter 9, Table 1: 53% for one conductor, 31% for two, 40% for over two, and 60% for a nipple not exceeding 24 inches under Chapter 9, Note 4. The smallest trade size returned is the first one in the table whose permitted area covers the total. Note that Table 1 applies to conductors of the same size; where sizes are mixed the code sends you to Note 6 and the same area arithmetic, which is what this does.

Worked example

With Raceway EMT (thin-wall steel), Insulation THHN / THWN-2 (90 C, the usual pick), Conductor size 12 AWG, How many of them 4, Trade size you have 1/2", Length of the run A real run — normal fill, this page works out 17.5% full of 40% allowed. Smallest raceway that takes this pull: 1/2" · 4 conductors are 0.053 in²

Area allowed in 1/2"0.122 in² of 0.304
Each 12 AWG conductor0.013 in²
Room left for more of the same size5

Sources:

The part fill percentage does not tell you

Bends beat percentage. The code limits total bends to 360 degrees between pull points, and a pull at 38% fill through four 90-degree bends is far harder than 40% through one. Plan pull boxes before you plan fill.

Fill and derating are two separate limits and both apply. Nine 12 AWG conductors fit in half-inch EMT and would all be derated to 70% of their ampacity, which usually removes the reason for putting them there.

Bigger pipe is nearly free at rough-in. The cost difference between half-inch and three-quarter is small; the cost of re-pulling a jammed run is a day.