Box Fill Calculator

Total the volume a device box needs under NEC 314.16(B), then check it against your box.

Insulated conductors (entering the box)

Devices (switches / receptacles)

Each yoke = 2× the largest conductor.

Support fittings (studs / hickeys)

Internal cable clamp(s) present (+1× largest)

Equipment grounds present (all = 1× largest)

Your box volume (cu in)

Volume required

Your box

How 314.16(B) counts

Each conductor through/terminating = 1 (by its size). All equipment grounds together = 1 (largest). All internal clamps together = 1 (largest). Each device yoke = 2 (largest conductor on it). Each support fitting = 1 (largest). Pigtails that don't leave the box don't count.

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