NEC Box Fill Calc

Run every single-box check free. Unlock one Rough-In Box Schedule to label up to 30 checks, put corrections first, and share or export the handoff.

NEC Box Fill Calc gives electricians a complete NEC 314.16(B) single-box field check at no charge. When a job spans multiple boxes, the existing Rough-In Schedule keeps labels and corrections together for a shareable handoff.

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 the Rough-In Box Schedule once to:

• Name the current project and label each box or room
• Collect up to 30 completed box checks on device
• See project totals for passing and overfilled boxes
• Put every required correction first, including overage, current box, and recommended replacement
• Reload any scheduled check into the free calculator
• Share or export one complete plain-text schedule
• 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.