TL;DR
Box fill is the calculated volume an electrical box must provide for the conductors, devices, clamps, and grounds inside it, tallied under NEC 314.16 in cubic inches: each 14 AWG counts 2.0 and each 12 AWG 2.25, a switch or receptacle counts as two conductors, all grounds together count as one (plus more for additional equipment grounding conductor sets), and internal clamps add one. Overstuffed boxes overheat, damage insulation, and crowd splices into failure, which is why the rule exists.
What it means
Box fill is the calculated volume an electrical box must provide for the conductors, devices, clamps, and grounds inside it, tallied under NEC 314.16 in cubic inches: each 14 AWG counts 2.0 and each 12 AWG 2.25, a switch or receptacle counts as two conductors, all grounds together count as one (plus more for additional equipment grounding conductor sets), and internal clamps add one. Overstuffed boxes overheat, damage insulation, and crowd splices into failure, which is why the rule exists. Standard single-gang nail-on boxes hold 18 to 22.5 cubic inches, quickly consumed when a circuit passes through plus feeds a three-way.
Where it sits in the glossary
Box fill 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.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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