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. All the equipment grounding conductors together count as one, also at the largest ground volume. 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.
All grounds count as one
Every equipment grounding conductor in the box together counts as a single volume under 314.16(B)(5), at the largest ground present. A second count is added only when you have isolated grounds.
Multiply by the largest-conductor volume
Use Table 314.16(B): 14 AWG is 2.0, 12 AWG is 2.25, 10 AWG is 2.5 cubic inches. Add conductors, clamps as one, supports as one, devices as two, and grounds as one, each at its volume, then compare to the box.
Device yoke counts two. All grounds count one. Multiply each by the largest-conductor volume.
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