Electrical Box Fill & Wire Capacity Calculator (NEC 314.16)
Calculate electrical box fill cubic inches, conductor allowances for 14 AWG and 12 AWG wire, device yokes, internal clamps, and NEC code compliance.
Calculated Results
Frequently Asked Questions
What is the NEC 314.16 electrical box fill calculation?
National Electrical Code (NEC 314.16) governs the maximum number of wires, devices, and fittings permitted in an electrical junction or outlet box to prevent wire insulation damage, overheating, and electrical fire hazards.
What are the cubic inch volume allowances for 14 AWG and 12 AWG wire?
Under NEC Table 314.16(B), each 14 AWG conductor requires 2.00 cubic inches of box volume. Each 12 AWG conductor requires 2.25 cubic inches. Each 10 AWG conductor requires 2.50 cubic inches.
How are duplex outlets and toggle switches counted in box fill?
Each device yoke (standard outlet or toggle switch) counts as a double conductor volume allowance based on the largest conductor connected to the device (e.g., 2 × 2.25 = 4.50 cu in for 12 AWG).
How do equipment grounding wires count towards box fill?
All equipment grounding wires count as one single allowance based on the largest ground wire for the first 4 grounds. For each additional ground wire over 4, add a 1/4 (0.25) allowance per the updated NEC 314.16(B)(5).