Match the actual products
Select the raceway schedule, insulation family, conductor size, and quantity. For a listed cable, use the manufacturer's actual outside diameter.
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Conduit Fill Chart & Calculator
Check a mixed run, find the maximum wire count, or choose the minimum conduit size—with the math shown.
EMTIMCRMCPVC 40/80THHN & XHHW
Conduit fill calculator
01
Build your raceway
02
9 totalAdd conductors or cables
Within fill limit. 39.4% used; 40 percent allowed. Minimum EMT 1/2 inches.
03
Within fill limitInstant fill check
1/2" EMT · 0.622" equivalent ID
Area-scaled schematic — not a physical pulling layout
39.4%fill used
40% allowedThree or more conductors
40% limit
0%100%
Occupied area0.120 in²
Allowed area0.122 in²
Minimum EMT1/2"
Max same-size count9
Field-friendly option3/4" EMTOne trade size above the calculated minimum when available
Fill check only. Grounds occupy fill. Current-carrying count, ampacity adjustment, environment, bends, and local amendments require a separate review.
Chapter 9 quick reference
The fill limit changes with conductor count
The tool chooses the governing column automatically and keeps the published allowable area separate from total raceway area.
153%conductor or cable
231%conductors or cables
3+40%standard raceway
≤24″60%eligible nipple only
Interactive reference
Conduit fill chart for maximum wire count
Same-size conductor capacities are generated by the same engine as the calculator. Select any number to load that exact configuration above.
Current selection Click to load
| Trade size | #14AWG | #12AWG | #10AWG | #8AWG | #6AWG | #4AWG | #3AWG | #2AWG | #1AWG | #1/0AWG | #2/0AWG | #3/0AWG | #4/0AWG |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/2"(16) | |||||||||||||
| 3/4"(21) | |||||||||||||
| 1"(27) | |||||||||||||
| 1-1/4"(35) | |||||||||||||
| 1-1/2"(41) | |||||||||||||
| 2"(53) | |||||||||||||
| 2-1/2"(63) | |||||||||||||
| 3"(78) | |||||||||||||
| 3-1/2"(91) | |||||||||||||
| 4"(103) |
*Count-specific limits still govern. A single conductor uses the 53% column, two use 31%, and three or more use 40%. Eligible nipples use 60%.
Same-size capacities include the Chapter 9 Note 7 ≥0.8 rounding rule. Mixed physical areas must be calculated above and are never rounded this way.
Transparent calculation
See exactly how this result is built
The calculator adds the published physical area of every conductor or cable, then compares that total with the selected raceway's published allowable area. It never treats fill as ampacity approval.
2026 reference basis: NFPA 70 Chapter 9 Table 1 and Notes 4, 7, and 9; Table 4 raceway areas; and Table 5 round concentric-lay THHN/XHHW areas. Compact conductors and Table 5A values are not assumed—use the listed manufacturer area or actual cable OD.
01
Add occupied areaQuantity × physical area for each conductor group.
02
Select the limit53% for one, 31% for two, 40% for three or more, or 60% for an eligible nipple.
03
Evaluate and sizeCompare areas, apply same-size Note 7 only when eligible, then scan upward for the minimum trade size.
Field workflow
From rough-in question to a defensible answer
Use the tool as a fast area check, then verify the conditions the fill calculation cannot know.
Read both answers
The minimum size is the calculated threshold. The field-friendly option is one trade size larger when available—often a better pull.
Complete the code review
Count grounds for fill, then separately check current-carrying conductors, adjustment factors, temperature, bends, pull tension, and local amendments.
Worked examples
Load a realistic case, then change it
Each example opens in the same calculator—no dead-end article or new page.
Common field questions
Conduit fill answers without the fine-print trap
These answers explain the scope behind the instant result. The authority having jurisdiction makes the final determination.
Run your configuration ↑Do ground wires count for conduit fill?＋
Yes. Equipment grounding and bonding conductors occupy physical space, so include them in the fill calculation. Whether a conductor counts as current-carrying for ampacity adjustment is a separate question.
Why are the limits 53%, 31%, and 40%?＋
The governing percentage depends on the number of conductors or cables in the raceway: 53% for one, 31% for two, and 40% for three or more. The calculator switches columns automatically.
When can I use the 60% nipple allowance?＋
Only for a raceway nipple no longer than 24 inches installed between boxes, cabinets, or similar enclosures. Connector length is not part of the 24-inch raceway length. Confirm that the actual installation qualifies.
How do I calculate mixed wire sizes?＋
Add the physical area of every conductor group, then compare the sum with the raceway's allowable area. Do not add capacities from a same-size chart, and do not use Note 7 rounding on a mixed physical-area set.
Does a fill PASS also cover ampacity derating?＋
No. Raceway fill and ampacity adjustment are separate checks. Neutral behavior, spares, nonlinear loads, ambient temperature, terminal ratings, and a qualifying nipple can all change the ampacity review.
What should I enter for Cat6, fiber, or a multiconductor cable?＋
Choose Custom cable OD and enter the listed manufacturer's actual outside diameter. For an elliptical cable, use its major diameter as the diameter of a circle. Cable constructions vary too much to infer safely from a category name.
Why can a same-size chart count slightly exceed the percentage?＋
Chapter 9 Note 7 allows the next whole same-size count when the unused decimal capacity is 0.8 or greater. The calculator labels this exception; it never applies that rounding to mixed physical areas.
Should I use the minimum size or the next size up?＋
The minimum is the area-based threshold. A larger raceway can reduce pulling difficulty and leave useful margin, especially with long runs, bends, large conductors, or a possible three-conductor jam condition.