NEC CH. 9, TABLE 1NEC 2026
Free NEC Conduit Fill Calculator
Determine conduit fill to NEC Chapter 9, Table 1 for any raceway and conductor combination. Overcrowded conduits trap heat, make pulls impossible, and violate the 40% fill limit for more than two conductors. Try the free demo below, then unlock the full conduit fill calculator with every trade size and wire type.
Why conduit fill matters
- NEC Chapter 9, Table 1 caps fill at 53% for one conductor, 31% for two, and 40% for three or more.
- Each conductor's area comes from Chapter 9, Table 5 (and Table 5A for compact strands).
- Exceeding the limit causes jamming, overheating, and derating that fails inspection.
BOX FILL CALCULATORDEMO
BOX TYPE (NEC 314.16)
4" Square × 1-1/2" Deep — 21 in³
CONDUCTOR
2
BOX-MOUNTED ITEMS
Device
1
EGC
1
NEC LIMIT 100%
COMPLIANT
FILL BREAKDOWN
2 × 14 AWG = 4.00 in³
1 × device (2× largest wire) = 4.00 in³
1 × EGC (1× largest EGC) = 2.00 in³
TOTAL FILL10.00 in³
REMAINING11.00 in³
Pro unlocks: multiple conductor groups, all box types, conduit fill (Ch. 9)
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