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Conduit Fill Calculator
Pick the conduit and how many conductors of what size are going in it. This returns the fill percentage and whether it passes the NEC limit for that number of conductors.
Your numbers
Result
Conduit fill
17.5
%
- NEC limit
- 40%
- Passes?1 = yes, 0 = no
- 1
- Max conductors this size
- 9wires
- Total conductor area
- 0.053sq in
- Allowable fill area
- 0.122sq in
- Conduit internal area
- 0.304sq in
How this is calculated
- Total conductor area = area per conductor × number of conductors.
- Fill % = total conductor area ÷ conduit internal area × 100.
- NEC Chapter 9 Table 1 limits: 53% for one conductor, 31% for two, 40% for three or more.
- Allowable area = conduit internal area × the limit for your conductor count.
Before you order
- The 31% figure for exactly two conductors is not a typo and catches people out — two conductors jam rather than nest, so the limit is tighter than for three.
- These are EMT areas. Rigid, IMC, PVC and flex all have different internal dimensions; use the right column of Table 4 for the raceway you are actually installing.
- Mixed conductor sizes: add each one's area individually rather than multiplying, and use the total.
- Fill is a pulling and heat limit. Passing on paper still leaves derating for more than three current-carrying conductors, and a long run with several bends can be unpullable at legal fill.
- Always verify against the current NEC and whatever your AHJ has amended. This is a check, not an authority.
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