Tools · Box Fill
Box Fill Calculator
Add up the required box volume per NEC 314.16(B) — conductors, devices, clamps, and grounds — and compare it to your box’s cubic-inch capacity.
How it’s calculated. NEC 314.16(B) volume allowances per conductor: 14 AWG = 2.00, 12 = 2.25, 10 = 2.50, 8 = 3.00, 6 = 5.00 in³. Each device/yoke counts as 2× the largest conductor; internal cable clamps add 1× the largest conductor; all equipment-grounding conductors together count as 1× the largest ground.
Conductors that both originate and terminate inside the box (pigtails) are not counted. Compare the required volume to the box’s marked cubic-inch capacity. This is an estimate — confirm against the box listing and the full design.
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