Conduit fill, checked against Chapter 9.
Add the conductors in the run and pick a trade size. The calculator totals conductor area from NEC Chapter 9 Table 5, compares it with the EMT area in Table 4 against the Table 1 limit, and finds the smallest EMT that passes.
- EMT ½" to 4"
- THHN / THWN-2
- 53 / 31 / 40% limits
- Smallest passing size
Conductors Count grounds too
Raceway
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Copy these results, then add your approved sample files in the trial brief.
Based on NEC Chapter 9 Tables 1, 4 and 5 for EMT and THHN/THWN-2. Other conduit types and insulations have different areas. Derating, nipples and the code edition your AHJ enforces are not covered here.
EMT internal area and 40% fill.
NEC Chapter 9, Table 4. The 40% column is the limit for three or more conductors.
| Trade size | Total area (in²) | 40% fill (in²) | #12 THHN max |
|---|---|---|---|
| ½" | 0.304 | 0.122 | 9 |
| ¾" | 0.533 | 0.213 | 16 |
| 1" | 0.864 | 0.346 | 26 |
| 1¼" | 1.496 | 0.598 | 45 |
| 1½" | 2.036 | 0.814 | 61 |
| 2" | 3.356 | 1.342 | 101 |
Three limits, one table.
Chapter 9, Table 1 sets the percentage of the raceway area conductors may occupy.
One conductor: 53%
A single conductor can fill just over half the raceway.
Two conductors: 31%
Lower than one or three, because two round conductors jam more easily.
Three or more: 40%
The everyday limit for branch circuits and feeders.
Count the ground
Equipment grounding and bonding conductors count toward fill.
Fill is one run. The bid is every run.
RenderDraw proposes conduit runs, device counts and panel schedule data from electrical drawings, with the source sheet on every row, for your estimator to approve before pricing.
- Source on every row. Each proposed quantity keeps the sheet and location it came from.
- Estimator approval before pricing. Your estimator accepts, corrects or rejects proposals; nothing is priced until it is approved.
- Addenda through the same review. Changed sheets go back through takeoff and estimator review.
- Your assemblies, your rates. Approved rows hand off to your assemblies, labor units and pricing inputs.
Conduit fill calculator, answered.
What is the maximum conduit fill?
Under NEC Chapter 9 Table 1: 53% of the raceway's area for one conductor, 31% for two, and 40% for three or more.
How many #12 THHN wires fit in ¾ inch EMT?
16. ¾" EMT has 0.533 in² of area, 40% is 0.213 in², and #12 THHN is 0.0133 in², which gives 16.03.
How many #12 wires fit in ½ inch EMT?
9 THHN/THWN-2 conductors, using the 40% limit on 0.304 in².
Do ground wires count toward conduit fill?
Yes. Equipment grounding and bonding conductors count. Use their actual size and insulation.
Does conduit fill include derating?
No. Fill limits how many conductors physically fit. Ampacity adjustment for more than three current-carrying conductors is a separate calculation under 310.15.
Send one plan set. Judge the result yourself.
A focused, no-obligation evaluation on your own drawings. Your sample files remain private while we assess the request.
- Upload one representative plan set (a legible PDF set is the most reliable starting point), plus an addendum if you have one.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with what was extracted, what was flagged for review, and the most useful next step.