Determine the required size for an electrical junction box per NEC 314.16 standards.
Box Components
Sizing Results
Enter component counts to calculate volume
About this calculator
Overview
NEC 314.16 defines 'Box Fill' requirements to prevent heat buildup and wire damage inside electrical boxes. Every wire, device, and clamp inside the box takes up a specific 'volume allowance' based on the wire gauge used.
💡
Pro Tips
Metal boxes usually have their cubic-inch capacity stamped inside.
If the box is too small, use a box extension (aka 'goof ring') to add legal volume.
Pigtails (wires that start and end inside the box) do not count toward volume allowances.
!
Fun Facts
"A standard duplex receptacle or switch counts as 2 volume allowances."
"Internal cable clamps count as 1 allowance (regardless of how many clamps there are)."
"All ground wires together count as 1 allowance for up to four wires, and 1/4 allowance for each additional wire."
Formula: Required Volume = Σ (Allowances × Unit Volume)
