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Electrical Box Fill Calculator

NEC 314.16 box fill from conductor count, devices, and box volume.

Inputs

Contents

Volume allowance per conductor from NEC 314.16(B): 2.00 for 14 AWG, 2.25 for 12 AWG, 2.50 for 10 AWG, 3.00 for 8 AWG, 5.00 for 6 AWG.

Count every conductor terminated or spliced inside the box.

Each yoke counts as two conductors (314.16(B)(4)); a double-gang device counts as four.

All equipment grounding conductors together are one allowance based on the largest (314.16(B)(5)).

One or more internal clamps count as a single allowance (314.16(B)(2)).

Box

Marked volume of the box.

Result

Box volume available
18.0 cu in
Margin (negative = undersized)
0.00 cu in
Within 314.16 (1 = yes)
1
Required box volume
18.00 cu in
Equivalent conductor count
8.0
Volume used
100.0 %
Most conductors of this size alone
8

What to check

  • Largest conductor size
  • Device count
  • Marked box volume

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Screening tool. Verify against the NEC as adopted locally, the AHJ, and nameplate data before acting.

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