Conduit Fill Calculator

Calculate conduit fill percentage per NEC Chapter 9. Supports EMT, IMC, and RMC conduit types.

Conduit Type

Conduit Size

Wire Type/Size

Number of Conductors

Results

Fill Percentage

3.2%

NEC limit 53% for 1 conductor

Max Conductors

at the 40% limit (3+ conductors)

Status

✓ COMPLIANT

Conduit Size Calculator: Find the Smallest Conduit for Your Wires

Add up the area of every conductor, then pick the smallest trade size whose fill stays at or under the NEC limit. For same-size THHN in EMT that gives, for example, three #12 in 1/2", ten #12 in 3/4", six #10 in 3/4" and four #4 in 1". The tool below does this for a mixed set, such as three hot conductors plus a smaller ground.

Conduit type

Conductor size

How many

3 conductors, total area 0.0399 in², NEC fill limit 40%

Smallest EMT: 1/2" (13.1% fill)

Trade size	Fill	Within 40%?
1/2"	13.1%	✓ Yes
3/4"	7.5%	✓ Yes
1"	4.6%	✓ Yes
1-1/4"	2.7%	✓ Yes
1-1/2"	2.0%	✓ Yes
2"	1.2%	✓ Yes

How to size conduit by hand

List every conductor, including the equipment grounding conductor. The NEC counts grounding and bonding conductors in conduit fill (see the notes to the Chapter 9 tables).
Add the areas. Multiply each conductor's area from Chapter 9, Table 5 by how many you have and add the results. For example, three #6 THHN plus one #10 THHN is 3 × 0.0507 + 0.0211 = 0.1732 in².
Pick the limit by count. One conductor 53%, two conductors 31%, three or more 40% (Chapter 9, Table 1). Here that is four conductors, so 40%.
Choose the smallest size whose usable area (its Table 4 interior area times the limit) is at least your total. That is the size the tool marks above.

This tool covers THHN conductors in 1/2" to 2" EMT, IMC, RMC and PVC. Other insulation types have different areas in Table 5, so do not use these results for them. Conduit fill is a space limit only; it does not set how much current the wires may carry, so check ampacity separately in the wire gauge chart. Verify against the NEC edition and local amendments that apply to your installation.

How Many THHN Conductors Fit? (Most-Searched EMT Sizes)

Quick answers for the combinations electricians look up most, at the NEC 40% fill limit for three or more same-size conductors. For example, 3/4" EMT holds up to ten #10 THHN and 1/2" EMT holds up to nine #12 THHN. Each cell shows the maximum conductor count and the fill percentage it reaches — computed from the same NEC cross-sectional areas the calculator above uses.

EMT trade size	#12 THHN	#10 THHN	#8 THHN
1/2" EMT	9 (39.2%)	5 (34.6%)	3 (36.0%)
3/4" EMT	16 (40.0%)	10 (39.6%)	5 (34.4%)
1" EMT	26 (40.0%)	16 (39.0%)	9 (38.1%)

All conductors the same size with THHN insulation, at the NEC Chapter 9, Table 1 40% fill limit for three or more conductors. For one or two conductors, use the calculator above (53% and 31% limits). Always verify against the NEC edition and any local amendments for your installation.

How Many Large THHN Conductors Fit? (#6 to 4/0 in 1"–2" Conduit)

Feeders and service conductors are the sizes people search for most: #6, #4, #2, #1, 1/0, 2/0, 3/0 and 4/0 THHN. At the NEC 40% fill limit for three or more same-size conductors, 2" EMT holds up to seven 1/0 THHN or four 4/0 THHN, and 1" EMT holds up to six #6 THHN but only one 1/0 or 4/0. The table shows the maximum count and the fill percentage it reaches, computed from the same NEC cross-sectional areas as the calculator above.

THHN size	1" EMT	1-1/4" EMT	1-1/2" EMT	2" EMT
#6 THHN	6 (35.2%)	11 (37.3%)	16 (39.9%)	26 (39.3%)
#4 THHN	4 (38.1%)	7 (38.6%)	9 (36.4%)	16 (39.3%)
#2 THHN	2 (26.8%)	5 (38.7%)	7 (39.8%)	11 (38.0%)
#1 THHN	2 (36.1%)	3 (31.3%)	5 (38.4%)	8 (37.2%)
1/0 THHN	1 (21.4%)	3 (37.2%)	4 (36.5%)	7 (38.7%)
2/0 THHN	1 (25.7%)	2 (29.7%)	3 (32.8%)	6 (39.8%)
3/0 THHN	1 (31.0%)	2 (35.8%)	3 (39.5%)	5 (39.9%)
4/0 THHN	1 (37.4%)	1 (21.7%)	2 (31.8%)	4 (38.6%)

Reading the large-conductor numbers

These are same-size counts. A conduit carrying mixed sizes (for example three 4/0 plus one #2 ground) must be checked by adding each conductor's area and comparing the total with the 40% area — the calculator above does this for one wire size at a time, so add the areas by hand for mixed sizes.
One or two conductors use different limits. A single conductor may fill 53% and two may fill 31% (NEC Chapter 9, Table 1), so a lone 4/0 fits comfortably in smaller conduit than the three-or-more table suggests.
Fill is not ampacity. Fitting the wires in the conduit says nothing about how much current they may carry; more than three current-carrying conductors in one raceway can require ampacity adjustment under NEC 310.15(C)(1). Check both.
Other conduit types differ slightly. The same sizes in rigid (RMC) or PVC Schedule 40 hold a similar number, and occasionally one fewer or one more (for example 2/0 THHN in 2": six in EMT and RMC, five in PVC Schedule 40). Switch the conduit type in the calculator to check the exact case.

THHN cross-sectional areas from NEC Chapter 9, Table 5 (including 3/0 = 0.2679 and 4/0 = 0.3237 in²); conduit areas from Table 4. Counts are 40% of the interior area ÷ one conductor's area, rounded down. Always verify against the NEC edition and local amendments that apply to your installation.

NEC Conduit Fill Requirements

Number of Conductors	Maximum Fill
1 conductor	53%
2 conductors	31%
3 or more conductors	40%

NEC Conduit Fill Chart — Max THHN Conductors (40% Fill)

The tables below show the maximum number of THHN conductors allowed in EMT, IMC, RMC, and PVC (Schedule 40 & Schedule 80) conduit by trade size, under the NEC Chapter 9 40% fill limit for three or more conductors of the same size. Every value is computed from the same conduit and wire cross-sectional areas this calculator uses (40% of the conduit's internal area ÷ one conductor's area, rounded down), so the chart and the calculator always agree — and the counts match NEC Annex C. For one or two conductors, size with the calculator above (53% and 31% limits), or check the NEC code reference.

PVC conduit fill: Schedule 40 vs Schedule 80

Rigid PVC comes in two wall thicknesses, and they do not hold the same number of wires. Schedule 80 has a thicker wall and a smaller interior, so it fits fewer conductors than Schedule 40 of the same trade size — always confirm which schedule you are running before you size the raceway. At the NEC 40% fill limit (three or more THHN conductors of one size):

3/4" PVC Sch 40 holds up to 15 #12 or 9 #10 THHN; the same size in Sch 80 holds 12 #12 or 7 #10.
1/2" PVC Sch 40 holds up to 8 #12 THHN; Sch 80 holds only 6 #12.

Both PVC schedules are included in the full chart below and in the calculator's conduit-type menu. Interior areas are from NEC Chapter 9, Table 4; counts are 40% of the interior area ÷ one conductor's area, rounded down.

EMT (Electrical Metallic Tubing)

AWG (THHN)	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
14 THHN	12	21	35	61	83	138
12 THHN	9	16	26	44	61	100
10 THHN	5	10	16	28	38	63
8 THHN	3	5	9	16	22	36
6 THHN	2	4	6	11	16	26
4 THHN	1	2	4	7	9	16
3 THHN	1	2	3	6	8	13
2 THHN	1	1	2	5	7	11
1 THHN	0	1	2	3	5	8
1/0 THHN	0	1	1	3	4	7
2/0 THHN	0	0	1	2	3	6
3/0 THHN	0	0	1	2	3	5
4/0 THHN	0	0	1	1	2	4

IMC (Intermediate Metal Conduit)

AWG (THHN)	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
14 THHN	14	24	39	67	91	151
12 THHN	10	17	28	49	66	110
10 THHN	6	11	18	31	42	69
8 THHN	3	6	10	18	24	40
6 THHN	2	4	7	12	17	28
4 THHN	1	2	4	7	10	17
3 THHN	1	2	3	6	9	15
2 THHN	1	2	3	5	7	12
1 THHN	0	1	2	4	5	9
1/0 THHN	0	1	2	3	4	7
2/0 THHN	0	1	1	2	4	6
3/0 THHN	0	0	1	2	3	5
4/0 THHN	0	0	1	2	2	4

RMC (Rigid Metal Conduit)

AWG (THHN)	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
14 THHN	12	22	36	62	85	140
12 THHN	9	16	26	45	62	102
10 THHN	5	10	16	28	39	64
8 THHN	3	5	9	16	22	37
6 THHN	2	4	7	12	16	26
4 THHN	1	2	4	7	10	16
3 THHN	1	2	3	6	8	14
2 THHN	1	1	3	5	7	11
1 THHN	0	1	2	3	5	8
1/0 THHN	0	1	1	3	4	7
2/0 THHN	0	0	1	2	3	6
3/0 THHN	0	0	1	2	3	5
4/0 THHN	0	0	1	1	2	4

PVC Schedule 40 (Rigid PVC)

AWG (THHN)	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
14 THHN	11	20	34	59	81	135
12 THHN	8	15	25	43	59	98
10 THHN	5	9	15	27	37	62
8 THHN	3	5	9	15	21	35
6 THHN	2	4	6	11	15	25
4 THHN	1	2	4	7	9	15
3 THHN	1	2	3	5	8	13
2 THHN	0	1	2	5	6	11
1 THHN	0	1	2	3	5	8
1/0 THHN	0	1	1	3	4	7
2/0 THHN	0	0	1	2	3	5
3/0 THHN	0	0	1	2	2	4
4/0 THHN	0	0	1	1	2	4

PVC Schedule 80 (Rigid PVC)

AWG (THHN)	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
14 THHN	8	16	28	51	70	118
12 THHN	6	12	20	37	51	86
10 THHN	4	7	13	23	32	54
8 THHN	2	4	7	13	18	31
6 THHN	1	3	5	9	13	22
4 THHN	1	1	3	6	8	13
3 THHN	0	1	2	5	7	11
2 THHN	0	1	2	4	5	9
1 THHN	0	1	1	3	4	7
1/0 THHN	0	0	1	2	3	6
2/0 THHN	0	0	1	2	3	5
3/0 THHN	0	0	1	1	2	4
4/0 THHN	0	0	0	1	2	3

Assumes all conductors are the same size with THHN insulation and the 40% fill limit from NEC Chapter 9, Table 1 (three or more conductors). A value of 0 means that conductor does not fit in that trade size at 40% fill. Trade sizes shown: 1/2" through 2". Always verify against the edition of the NEC and any local amendments that apply to your installation.