TL;DR
A box fill calculation is the arithmetic an electrician performs under NEC 314.16(B) to verify that a chosen box has enough cubic-inch volume for everything entering it, summing volume allowances by wire gauge for conductors, devices, clamps, support fittings, and equipment grounds. The allowance per conductor scales with gauge, from 2.0 cubic inches at 14 AWG to 2.5 at 10 AWG, and the largest conductor present sets the allowance for devices and grounds.
What it means
A box fill calculation is the arithmetic an electrician performs under NEC 314.16(B) to verify that a chosen box has enough cubic-inch volume for everything entering it, summing volume allowances by wire gauge for conductors, devices, clamps, support fittings, and equipment grounds. The allowance per conductor scales with gauge, from 2.0 cubic inches at 14 AWG to 2.5 at 10 AWG, and the largest conductor present sets the allowance for devices and grounds. It is performed at rough-in, before boxes are nailed up, since the cure for a failed count is a deeper box or an extension ring. Plan reviewers and inspectors spot-check it where multiple cables converge, such as three-way switch locations.
Where it sits in the glossary
Box fill calculation is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
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See also
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