Pick the conduit type and trade size, then add up to four groups of conductors, and get the fill percent against the NEC limit, whether it passes, and the smallest trade size that does. Or choose one wire size and get the most conductors that fit. Uses NEC Chapter 9 Tables 1, 4 and 5 for THHN and XHHW.
Worked example
These are example values. Change any entry above and press Calculate to run your own numbers.
Within the NEC fill limitArea to spare: 0.1176 in²
Smallest EMT size that passes
1/2"at this fill limit
Include every conductor in the conduit, equipment grounding conductors too. Bare conductors use NEC Table 8, which this tool does not cover.
Figures are from NFPA 70 (NEC) 2017 Edition, Chapter 9, Tables 1, 4 and 5. Confirm against the edition your authority adopts. This tool does not cover derating, bends, nipples, conduit bodies or other code rules, and is not a substitute for the code or a qualified electrician.
How it works
The National Electrical Code limits how much of a conduit's cross-section the conductors may fill, so they can be pulled in and can shed heat. The limit is 53% for one conductor, 31% for two and 40% for three or more. The calculator adds up the area of every conductor from Chapter 9 Table 5 and compares it with the matching share of the conduit area from Table 4.
The formulas
Fill % = total conductor area ÷ conduit internal area × 100
Limit: 1 conductor 53%, 2 conductors 31%, 3 or more 40% (NEC Chapter 9, Table 1)
Most conductors of one size = 40% of the conduit area ÷ the area of one conductor
Note 7: for same-size conductors, a result with a fraction of 0.8 or more rounds up to the next whole conductor
Conductor and conduit areas come from NEC Chapter 9, Tables 4 and 5
Reference tables
Conduit fill chart: most THHN conductors in EMT (40% fill)
Wire size
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
1
4
7
12
16
26
46
69
91
116
4 AWG
1
2
4
7
10
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
1
1
1
4
5
8
15
22
29
37
1/0 AWG
0
1
1
3
4
7
12
19
25
32
2/0 AWG
0
1
1
2
3
6
10
16
20
26
3/0 AWG
0
1
1
1
3
5
8
13
17
22
4/0 AWG
0
0
1
1
1
4
7
11
14
18
Three or more same-size THHN/THWN conductors in EMT, NEC Chapter 9 Tables 4 and 5 (2017 edition), with the Note 7 round-up. Charts for the 53% and 31% single and two-conductor limits, and for other conduit types and XHHW, are on the calculator above. Confirm against the edition your authority adopts.
EMT dimensions and fill areas (NEC Chapter 9, Table 4)
Trade size
Internal diameter (in)
Total area (in²)
53% (in²)
40% (in²)
31% (in²)
1/2"
0.622
0.304
0.161
0.122
0.094
3/4"
0.824
0.533
0.283
0.213
0.165
1"
1.049
0.864
0.458
0.346
0.268
1 1/4"
1.38
1.496
0.793
0.598
0.464
1 1/2"
1.61
2.036
1.079
0.814
0.631
2"
2.067
3.356
1.778
1.342
1.04
2 1/2"
2.731
5.858
3.105
2.343
1.816
3"
3.356
8.846
4.688
3.538
2.742
3 1/2"
3.834
11.55
6.119
4.618
3.579
4"
4.334
14.75
7.819
5.901
4.573
Conductor areas, THHN/THWN and XHHW (NEC Chapter 9, Table 5)
Size
THHN/THWN (in²)
XHHW (in²)
14 AWG
0.0097
0.0139
12 AWG
0.0133
0.0181
10 AWG
0.0211
0.0243
8 AWG
0.0366
0.0437
6 AWG
0.0507
0.059
4 AWG
0.0824
0.0814
3 AWG
0.0973
0.0962
2 AWG
0.1158
0.1146
1 AWG
0.1562
0.1534
1/0 AWG
0.1855
0.1825
2/0 AWG
0.2223
0.219
3/0 AWG
0.2679
0.2642
4/0 AWG
0.3237
0.3197
250 kcmil
0.397
0.3904
300 kcmil
0.4608
0.4536
350 kcmil
0.5242
0.5166
400 kcmil
0.5863
0.5782
500 kcmil
0.7073
0.6984
600 kcmil
0.8676
0.8709
700 kcmil
0.9887
0.9923
750 kcmil
1.05
1.053
800 kcmil
1.109
1.112
900 kcmil
1.231
1.235
1000 kcmil
1.348
1.352
Frequently asked questions
How many 12 AWG wires fit in a 3/4 inch EMT conduit?
Sixteen THHN conductors of 12 AWG fit in 3/4 inch EMT at the 40% limit. In 1/2 inch EMT the limit is nine, and in 1 inch EMT it is 26. XHHW insulation is a little bulkier, so the same conduit holds fewer.
What is the NEC conduit fill limit?
NEC Chapter 9, Table 1 allows 53% of the conduit area for one conductor, 31% for two, and 40% for three or more. These limits assume a straight run and ordinary conditions. Other rules, such as those for nipples, lead-sheathed cable and some raceway types, set different figures.
What is Note 7 and why does the answer sometimes round up?
Note 7 to the Chapter 9 tables says that when all the conductors are the same size and the number that fits works out at 0.8 or more above a whole number, you may round up. Six 8 AWG THHN conductors in 3/4 inch EMT is an example: the arithmetic gives 5.82 and the note permits six. The calculator applies this only for a single group of one size.
Do I count the grounding conductor?
Yes. Chapter 9 Note 3 requires equipment grounding and bonding conductors to be included when you calculate fill. Add them as another group of conductors. Bare conductors use Table 8 areas, which this calculator does not cover.
Why does this chart sometimes differ by one from other charts?
For a single conductor or a pair, a few published conduit fill charts round the result differently from the strict Table 1 limit. This calculator uses the printed Table 1 percentages, so where the 53% or 31% column governs it can show a lower count. For three or more conductors, the common case, the figures match the usual charts.
Does this cover conduit longer or shorter than a normal run?
No. A conduit nipple of 24 inches or less may be filled to 60% under Chapter 9 Note 4, and this tool does not apply that. It also does not cover derating for more than three current-carrying conductors, pulling tension, bends, or conduit bodies. Use the code and a qualified electrician for those.
