NEC conduit fill: chart and calculation
Conduit fill questions ask how many conductors fit in a raceway, or which raceway size a group of conductors needs. Every answer comes from Chapter 9: Table 1 sets the percentage, Table 4 gives the raceway area and Table 5 gives each conductor area.
A timed 80-question exam in the ICC R17 format on the 2023 NEC, or your state’s exact format. Every answer has a worked explanation.
Or start with the free box and conduit fill drillWatch worked examples, step by step
The 314.16 box fill and Chapter 9 conduit fill methods, worked through 11 questions.
Fill percentage: Chapter 9, Table 1
| Number of conductors | Maximum fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| Over 2 | 40% |
Equipment grounding and bonding conductors count toward fill (Note 3). Nipples 24 in. or shorter may be filled to 60% (Note 4).
EMT areas: Chapter 9, Table 4
| Trade size | Total area (in²) | 40% area (in²) |
|---|---|---|
| 1/2 | 0.304 | 0.122 |
| 3/4 | 0.533 | 0.213 |
| 1 | 0.864 | 0.346 |
| 1-1/4 | 1.496 | 0.598 |
| 1-1/2 | 2.036 | 0.814 |
| 2 | 3.356 | 1.342 |
THHN and THWN-2 areas: Chapter 9, Table 5
| Size (AWG) | Area (in²) |
|---|---|
| 14 | 0.0097 |
| 12 | 0.0133 |
| 10 | 0.0211 |
| 8 | 0.0366 |
| 6 | 0.0507 |
| 4 | 0.0824 |
| 3 | 0.0973 |
| 2 | 0.1158 |
| 1 | 0.1562 |
| 1/0 | 0.1855 |
Practice conduit fill on a timed exam
A timed 80-question exam in the ICC R17 format on the 2023 NEC, or your state’s exact format. Every answer has a worked explanation.
Or start with the free box and conduit fill drillWorked examples
How many 12 AWG THHN fit in 3/4 in. EMT?
- More than two conductors, so 40% fill applies. 3/4 in. EMT 40% area = 0.213 in².
- 12 AWG THHN area = 0.0133 in².
- 0.213 ÷ 0.0133 = 16.0, so 16 conductors.
Sizing a raceway for mixed conductors
Three 6 AWG and one 10 AWG THHN in EMT
- Area: 3 × 0.0507 + 1 × 0.0211 = 0.1732 in².
- More than two conductors: compare with the 40% column.
- 3/4 in. EMT allows 0.213 in², so 3/4 in. is the minimum size.
Rounding: Note 7
When every conductor is the same size, Note 7 to Table 1 lets you round a result of 0.8 or more up to the next whole number. A result below 0.8 is rounded down. For mixed sizes, compare total area with the allowed area instead.
Informative Annex C lists the same-size answers for each raceway type, so you can check a calculation quickly during an open-book exam.
Common questions
What is the maximum conduit fill for three or more wires?
40% of the raceway area (Chapter 9, Table 1).
Do ground wires count in conduit fill?
Yes. Equipment grounding and bonding conductors are included in the fill calculation (Chapter 9, Note 3).
Where do I find how many wires fit in a conduit?
Informative Annex C gives the maximum number of same-size conductors for each raceway type and size.
Practice conduit fill on a timed exam
A timed 80-question exam in the ICC R17 format on the 2023 NEC, or your state’s exact format. Every answer has a worked explanation.
Or start with the free box and conduit fill drillMore journeyman exam guides
Section numbers follow the 2023 National Electrical Code (NFPA 70). Independent preparation, not affiliated with NFPA, ICC, PSI, Prometric, Pearson VUE or any state board.