Use our Box Fill Calculator to determine the minimum required volume for electrical boxes according to National Electrical Code (NEC) Article 314.16. Prevent overfilling, ensure safety, and pass inspections by accurately calculating wire, device, and clamp allowances. Essential for electricians and DIY projects for safe electrical installations.
Formula:
The total box fill volume is the sum of allowances for:
- Conductors: Each hot, neutral, or switched leg conductor counts for its specific volume allowance (e.g., 14 AWG = 2.0 cu in, 12 AWG = 2.2 cu in).
- Equipment Grounding Conductors: All grounding conductors combined count as one conductor volume allowance based on the largest conductor entering the box.
- Devices: Each single-gang device (switch, receptacle) counts as two conductor volume allowances based on the largest conductor entering the box.
- Internal Clamps: Each internal cable clamp counts as one conductor volume allowance based on the largest conductor entering the box.
- Support Fittings: Each support fitting (e.g., hickey) counts as one conductor volume allowance based on the largest conductor entering the box.