Free Tool · NEC Chapter 9
Conduit fill calculator
Tell it your cable and how many runs, and it gives you the smallest code-compliant EMT size, with the NEC math shown so you can check it.
Optional. Overrides the preset. Use the number on your cable's spec sheet.
Smallest compliant EMT
1-1/4" EMT
12 cables at 0.24 in OD fill it to 36.3%, under the 40.0% limit for three or more cables.
The math
- One cable: π × (0.24 ÷ 2)² = 0.0452 in²
- 12 cables: 0.0452 in² × 12 = 0.5429 in²
- Fill limit: 40.0% (NEC Chapter 9, Table 1)
| EMT | Total area | Allowed at 40.0% | Your fill | Result |
|---|---|---|---|---|
| 1/2" | 0.304 in² | 0.122 in² | 178.6% | Over limit |
| 3/4" | 0.533 in² | 0.213 in² | 101.9% | Over limit |
| 1" | 0.864 in² | 0.346 in² | 62.8% | Over limit |
| 1-1/4" | 1.496 in² | 0.598 in² | 36.3% | Fits |
| 1-1/2" | 2.036 in² | 0.814 in² | 26.7% | Fits |
| 2" | 3.356 in² | 1.342 in² | 16.2% | Fits |
Planning aid, not a substitute for a licensed electrician or your authority having jurisdiction. Figures come from NEC 2023 (NFPA 70), Chapter 9, Table 1 (fill percentages) and Table 4 (EMT areas, 1/2" through 2"). Cable diameters vary by manufacturer and jacket rating, so enter the OD from your spec sheet. The 60% allowance for a nipple (a raceway 24 inches or shorter, Chapter 9 Note 4) is deliberately not applied, so results are conservative for short sleeves. Verify against the edition of the code your jurisdiction has adopted.
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Request a cabling quoteHow many network cables fit in EMT (at the NEC Table 1 limit)
Counts honour NEC Chapter 9, Table 1: 53% for one cable, 31% for exactly two, and 40% for three or more. Nominal cable diameters shown; verify against your spec sheet.
| EMT | Total area | 40% area | Cat6 | Cat6a |
|---|---|---|---|---|
| 1/2" | 0.304 in² | 0.122 in² | 2 | 1 |
| 3/4" | 0.533 in² | 0.213 in² | 4 | 1 |
| 1" | 0.864 in² | 0.346 in² | 7 | 3 |
| 1-1/4" | 1.496 in² | 0.598 in² | 13 | 6 |
| 1-1/2" | 2.036 in² | 0.814 in² | 18 | 8 |
| 2" | 3.356 in² | 1.342 in² | 29 | 13 |
Common questions
How many Cat6 cables fit in 3/4" EMT?
Four, at the 40% fill limit. A Cat6 cable at 0.24 inch outer diameter is about 0.0452 in² each. 3/4" EMT has 0.533 in² total area, and 40% of that is 0.213 in². Dividing 0.213 by 0.0452 gives 4.7, and you round down, so four Cat6 fit. For twelve Cat6 you need 1-1/4" EMT. Use the calculator above for your exact count.
What fill percentage does the NEC allow?
Per NEC Chapter 9, Table 1: 53% for one cable, 31% for exactly two cables, and 40% for three or more. Structured cabling runs almost always fall under the 40% rule.
Does a 4-pair Cat6 cable count as 8 conductors?
No. Per NEC Chapter 9, Table 1, Note 9, a multiconductor cable counts as a single conductor for fill, using the overall cable diameter. A 4-pair Cat6 is one "cable" in the fill math, not eight.
Why does this calculator disagree with some others online?
Some published tools contain errors, such as claiming twelve Cat6 fit in 3/4" EMT (that is over 100% fill, which is physically impossible). This calculator uses the exact NEC Chapter 9 Table 4 areas and Table 1 limits, and shows every calculation so you can verify it against the code book.
Is this a substitute for an electrician or inspector?
No. It is a planning aid. Cable diameters vary by manufacturer and jacket rating, and jurisdictions adopt different code editions. Always verify against the adopted code and your authority having jurisdiction.
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