Input Parameters
About This Calculator
- NEC 314.16(B): per-conductor volume
- Device = 2× largest wire allowance
- Ground = 1× (all grounds combined)
How this box fill calculator works
NEC 314.16 assigns volume per conductor based on wire gauge. Total fill = (conductors + devices×2 + clamps + 1 ground) × volume allowance.
The total must not exceed the box's marked volume.
FAQ
How to calculate box fill?
Count items × volume per wire size.
NEC allowances?
#14: 2.0, #12: 2.25, #10: 2.5 in³ per item.
Standard box capacity?
4×4×1.5" = 18 in³, holds ~9× #12 wires.