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Electrical Box Fill Calculator

Construction
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Calculates the minimum required size of an electrical box based on the number and type of conductors and devices within the box, according to the National Electrical Code (NEC).

How To Use

How to use this calculator

Start with your values, or try a preset.

Step 1

Enter Number of 14 AWG wires, Number of 12 AWG wires, Number of 10 AWG wires, Number of devices (switches, receptacles), Number of internal cable clamps, and Number of ground wires in the units shown.

Step 2

Read Volume for ground wires, Volume for clamps, Volume for devices, Volume of 10 AWG wires, Volume of 12 AWG wires, Volume of 14 AWG wires, and Total Minimum Volume Required in the results panel. Results update as you change the inputs.

Step 3

Choose a preset to load an example, then adjust the values for your situation.

Worked Examples

Example calculations

See the inputs and their calculated results.

Single Gang Switch Box - 12 AWG

Number of 14 AWG wires: 0; Number of 12 AWG wires: 3; Number of 10 AWG wires: 0; Number of devices (switches, receptacles): 1; Number of internal cable clamps: 1; Number of ground wires: 1

Volume for ground wires: 0 cubic inches; Volume for clamps: 0 cubic inches; Volume for devices: 2 cubic inches; Volume of 10 AWG wires: 0 cubic inches; Volume of 12 AWG wires: 6.75 cubic inches; Volume of 14 AWG wires: 0 cubic inches; Total Minimum Volume Required: 8.75 cubic inches

Single Gang Receptacle Box - 12 AWG

Number of 14 AWG wires: 0; Number of 12 AWG wires: 4; Number of 10 AWG wires: 0; Number of devices (switches, receptacles): 1; Number of internal cable clamps: 1; Number of ground wires: 1

Volume for ground wires: 0 cubic inches; Volume for clamps: 0 cubic inches; Volume for devices: 2 cubic inches; Volume of 10 AWG wires: 0 cubic inches; Volume of 12 AWG wires: 9 cubic inches; Volume of 14 AWG wires: 0 cubic inches; Total Minimum Volume Required: 11 cubic inches

Two Gang Switch Box - 12 AWG

Number of 14 AWG wires: 0; Number of 12 AWG wires: 6; Number of 10 AWG wires: 0; Number of devices (switches, receptacles): 2; Number of internal cable clamps: 2; Number of ground wires: 2

Volume for ground wires: 0 cubic inches; Volume for clamps: 0 cubic inches; Volume for devices: 4 cubic inches; Volume of 10 AWG wires: 0 cubic inches; Volume of 12 AWG wires: 13.5 cubic inches; Volume of 14 AWG wires: 0 cubic inches; Total Minimum Volume Required: 17.5 cubic inches

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