Short answer: Box fill is a count. Add up the allowances under 314.16(B), multiply by the volume per conductor you read from the table in 314.16(B), and compare the result with the box volume from Table 314.16(A) or the box marking. Conduit fill is a division. For more than two conductors, read the raceway area from the 40% column of Chapter 9, Table 4, divide by the conductor area from Chapter 9, Table 5, and round down. When every conductor is the same size, Informative Annex C gives the count directly.
On the Texas Journeyman exam, the Calculation part gives you 110 minutes for 26 items, so practice finding the correct fill table and completing the count without spending too long on one question. The Practice Pack includes 10 timed two-part mocks, with 59 questions in 130 minutes and 26 in 110 minutes. Scores by part and topic help you identify areas to review, including questions involving table lookups. It also has 299 step-by-step calculation solutions, code-book navigation aids and a ranked tab-these-first list. US$39, one payment.
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Box fill: count the allowances first
Most box fill misses come from the count, not the math. Count each item once, the way 314.16(B) counts it, before you open any volume table.
| What is in the box | Allowances | Where to read it |
|---|---|---|
| Each conductor that 314.16(B)(1) counts, such as one that enters and ends or is spliced in the box (read the full list in your book) | 1 each | 314.16(B)(1) |
| All internal cable clamps, taken together | 1 total | 314.16(B)(2) |
| Each device yoke | 2, using the largest conductor on that yoke | 314.16(B) |
| Equipment grounding conductors, up to four | 1 total | 314.16(B)(5) |
| Each equipment grounding conductor beyond four | 1/4 each | 314.16(B)(5) |
Then work it in this order:
- Count allowances with the table above.
- Read the volume per conductor for the conductor size from the table in 314.16(B). That table was renumbered in 2026, so find it by reading the table title in your code book.
- Multiply allowances by the volume per conductor.
- Read the box volume from Table 314.16(A) or from the marking the question gives you, and compare.
Worked example with round example numbers: 6 insulated conductors enter and are spliced in the box, so all 6 are counted under 314.16(B)(1), excluding equipment grounding conductors. The same box also has internal cable clamps, one device yoke and 3 equipment grounding conductors, giving 6 + 1 + 2 + 1 = 10 allowances. If the question used an example volume of 1.0 cubic inch per conductor, the box would need 10 cubic inches. On the real exam you read the volume from your code book.
The two traps the workbook flags: counting each ground separately, and forgetting that a device yoke counts as two.
Conduit fill: area divided by area
Chapter 9, Table 1 sets the percent of the raceway you may fill:
| Number of conductors | Fill allowed |
|---|---|
| 1 | 53% |
| 2 | 31% |
| More than 2 | 40% |
For the usual exam question with more than two conductors:
- Open Chapter 9, Table 4 for the raceway type and trade size, and read the 40% column.
- Open Chapter 9, Table 5 for the conductor’s insulation type and size, and read its area.
- Divide the 40% area by the conductor area.
- Round down to a whole conductor, except that Note (7) allows a same-size conductor result with a decimal of .8 or more to round up.
Note (7) to the Chapter 9 tables covers same-size conductors: a result with a decimal of .8 or more rounds up. For same-size conductors, Informative Annex C gives the count without any math, which is faster when the question fits it.
Worked example with round example numbers: an example 40% area of 1.0 square inch divided by an example conductor area of 0.3 square inch gives 3.33, so 3 conductors. An example result of 7.85 with all conductors the same size has a decimal of .85, so Note (7) rounds it up to 8.
The trap: dividing the full raceway area instead of the 40% area.
Why fill is worth a tab
In our workbook’s 486 questions, Article 314 was cited 24 times and Article 300 19 times, which puts both in the top ten of its tab list. The PSI bulletin allows only permanent tabs made or provided by the NEC publisher, and no marking during the exam, so learn where Chapter 9 sits in your book before test day. Your calculator must be silent, battery-operated and non-programmable, and all conductors are copper unless the question says otherwise.
Check a box or a raceway
Box fill and conduit fill check
Enter your own count. The volume per conductor, box volume and both areas are example numbers to replace with the values you read from your code book.
- Insulated conductors counted under 314.16(B)(1) in your book, excluding equipment grounding conductors
- Internal cable clamps present (1 = yes, 0 = no)
- Device yokes in the box
- Equipment grounding conductors in the box
- Volume per conductor from the table in 314.16(B) (your book)
- Box volume from Table 314.16(A) or the marking (your book)
- Raceway area, 40% column of Chapter 9 Table 4 (your book)
- Conductor area from Chapter 9 Table 5 (your book)
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Texas Journeyman Electrician Exam Prep 2026 NEC (paperback)
Our own workbook has a conduit and box fill lesson among its 8 calculation method lessons, with worked calculations, code book lookup paths and the traps that lead to each wrong choice. Its 20-article tab list shows where 314 and 300 rank.
Do ground wires count in box fill?
Yes. Under 314.16(B)(5), up to four equipment grounding conductors count as one allowance together, and each additional equipment grounding conductor adds a quarter allowance. Apply this rule instead of counting every equipment grounding conductor as a full allowance.
What percent can a conduit be filled on the journeyman exam?
Chapter 9, Table 1 allows 53% for one conductor, 31% for two and 40% for more than two. When the question has more than two conductors, read the 40% column of Chapter 9, Table 4.
Where is the box fill volume per conductor in the 2026 NEC?
It is in the table in 314.16(B), which was renumbered in 2026, so read the table title in your code book. The box volume itself comes from Table 314.16(A) or from the box marking.
