Box Fill Calculator
Calculate electrical box volume requirements per NEC 314.16. Ensure adequate space for devices and wires.
Quick Presets
Box Type & Size
Devices
Wires
Box Fill Calculation
48.6%
NEC Compliant
Total Required
8.75 in³
Box Capacity
18.00 in³
Device Volume
2.00 in³
Wire Volume
6.75 in³
Available Space
9.25 in³
Maximum Capacity
Common Wire Sizes (this box):
1 AWG3 max
2 AWG3 max
3 AWG3 max
4 AWG3 max
Device Capacity:
Receptacle (15A/20A)9 max
GFCI Receptacle9 max
Single Pole Switch9 max
NEC Guidelines
NEC 314.16(B): Box fill requirements
• Each device/fitting = 2.0 in³
• Wire volume based on largest conductor
• Equipment grounding conductors count as one conductor
• Cable clamps, fixture studs add volume
⚠️ This calculator is for reference only. Always verify with local AHJ and current NEC requirements.