NEC 314.16NEC 2026
Free NEC 314.16 Box Fill Calculator
Calculate box fill to NEC 314.16 in seconds. Enter your conductors, devices, and equipment grounding conductors to verify the box isn't overfilled before you land wires. Overfilled boxes cause overheating, damaged insulation, and failed inspections — the demo below shows exactly how the full tool breaks down every volume allowance.
Why box fill matters
- NEC 314.16 limits the number and size of conductors, devices, and clamps allowed in a box.
- Each item counts as a volume allowance based on the largest conductor in the box.
- Exceeding the box's volume capacity risks overheating, insulation damage, and rejected inspections.
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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