NEC Box Fill Calc

Catch an overfilled box before rough-in inspection fails. Free field checks stay open. Unlock saved inspection cards, sharing, export, and restore once.

Catch an overfilled box before rough-in inspection fails.

NEC Box Fill Calc helps electricians run a fast NEC 314.16(B) field check on site, see exactly where the volume went, and spot the smallest listed box that fits before rework starts.

Free field check:

• Add conductors by gauge from 18 AWG through 6 AWG
• Count grounding conductors, internal clamps, support fittings, and devices correctly
• See total fill, pass/fail status, line-by-line breakdown, and the smallest listed standard box that fits
• Switch between 20 standard box sizes or enter a custom marked volume
• Work fully offline with no account, ads, or subscription

Unlock Inspection Cards once to:

• Save inspection cards on device
• Pin important cards for repeat rough-in work
• Reload a saved card back into the free check workflow
• Share or export a plain-text inspection summary
• Restore lifetime access on another device

Built for electricians, apprentices, and foremen who want to avoid repulls, box swaps, and inspection-day surprises.

Important:

• Always verify the enclosure's marked volume and local requirements on site.
• This app is a practical field aid, not a substitute for code judgment or inspection approval.