509 Box Fill: NEC 314

Calculate box fill per NEC 314.16 and pull/junction-box minimum dimensions per NEC 314.28 in seconds. 509 Box Fill is a fast, local-first field calculator built for electricians, journeymen, and apprentices. Enter conductor counts, clamp and device allowances, and equipment grounds to get the required cubic-inch fill and pass/fail status against a standard or custom box volume. Switch to Min Box to find the smallest standard box that fits. Use Pull Box to calculate minimum box dimensions for straight and angle/U-pull raceway entries. Designed for quick use: • NEC 314.16(B) conductor volume allowances • NEC 314.16(A) standard box volumes with pass/fail result • Min Box recommends the smallest standard box that fits • NEC 314.28 pull and junction box sizing for straight and angle/U pulls • Light and dark mode • Suite accent color picker • NEC reference citations on every work line • Local-first settings; no account or sign-in required 509 Box Fill is a field calculator. Always verify against the NEC adopted in your jurisdiction.