How do I count devices and grounds for box fill?
A device or yoke counts as two, at the volume of the largest conductor connected to it. Up to four equipment grounding conductors together count as one, at the largest ground volume, and each beyond four adds a quarter. Those two rules trip up most people. Count each as a unit, multiply by the right volume, and the box fill holds.
Last reviewed June 2026 · Answered by JourneymanIQ staff
Each device yoke counts twice
Under 314.16(B)(4) a strap or yoke, like a receptacle or switch, counts as two conductor volumes, based on the largest conductor connected to that device. Not one, two.
Up to four grounds count as one
Under 314.16(B)(5), up to four equipment grounding conductors together count as a single volume, at the largest ground; each one beyond four adds a quarter. Isolated grounds count the same way, with no separate allowance.
Give each count its volume
Use the volume table in 314.16(B): 14 AWG is 2.0, 12 AWG is 2.25, 10 AWG is 2.5 cubic inches. Add conductors at their own size, clamps as one and each type of support fitting as one at the largest conductor, devices as two at the largest conductor connected to them, and up to four grounds as one at the largest ground, then compare to the box.
Device yoke counts two. Up to four grounds count one. Give each count its own volume.
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