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Calculate the required electrical box volume under NEC 314.16. Counts conductors, devices, clamps, and grounds to tell you if your box is large enough.
Ask questions about your calculation results
3 free questions per session
AI provides general information, not financial advice. Always consult a qualified professional.
NEC 314.16 assigns a volume allowance to everything inside an outlet or device box, then requires the box to be at least that large. Each conductor gets a volume based on its size, each device yoke counts as two conductors, all internal clamps together count as one, and all equipment grounding conductors together count as one.
This calculator adds those allowances and compares the total to your box volume so you know whether the box is legal before you make up the splices.
From NEC Table 314.16(B): 14 AWG is 2.00 cubic inches, 12 AWG is 2.25, 10 AWG is 2.50, 8 AWG is 3.00, and 6 AWG is 5.00. When conductors are different sizes, each is counted at its own value, and clamp, device, and ground allowances use the largest conductor present.
People forget that a device yoke counts as two, that all grounds together still add one full conductor volume, and that pigtails entirely inside the box are not counted. Get the count right and an overcrowded box becomes obvious before it fails inspection.
Yes. All equipment grounding conductors together count as one conductor volume, based on the largest grounding conductor in the box.
Each device yoke or strap counts as two conductor volumes based on the largest conductor connected to it. A single receptacle on 12 AWG adds 4.5 cubic inches.
No. Conductors that begin and end inside the box, such as pigtails, are not counted. Only conductors that enter the box are counted.
Each 12 AWG conductor is 2.25 cubic inches under NEC Table 314.16(B).
Use a deeper or larger box, add a box extender to gain volume, or reduce the number of conductors and devices in that box.