Free calculator · AstralLearn
Box fill calculator
Count what's in the box — conductors, clamps, devices, grounds — and see whether it fits the box you picked, per NEC 314.16.
Back to AstralLearnConductors entering the box
×
Fits
22.5 in³box 30.3 in³ · 74%
- Conductors
- 13.5 in³
- Clamps
- 2.25 in³
- Devices
- 4.5 in³
- Supports
- 0 in³
- Grounds
- 2.25 in³
Volumes count by the largest conductor present (12 AWG) per NEC 314.16(B).
How it works (NEC 314.16(B)): each conductor entering = 1 volume of its size; all clamps together = 1 of the largest; each support fitting = 1; each device yoke = 2; all grounds together = 1 of the largest ground. The total must not exceed the box's marked volume.
Educational reference — verify against the current NEC and your AHJ. Need it inspected and permitted? Call a licensed C-10 → (650) 562-8594.
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