12 AWG Wire Box Fill
12 AWG conductors are required for 20-amp circuits and kitchen/bathroom outlets.
2.25
cu.in. per conductor
36.9
mm³ per conductor
20A
Max Ampacity
Common Applications
Box Capacity for 12 AWG
Maximum number of 12 AWG conductors that fit in common electrical boxes (conductors only, not accounting for devices, clamps, or grounds).
| Box Type | Volume | Max 12 AWG* |
|---|---|---|
| 4" Square x 1-1/4" Deep | 18 cu.in. | 8 |
| 4" Square x 1-1/2" Deep | 21 cu.in. | 9 |
| 4" Square x 2-1/8" Deep | 30.3 cu.in. | 13 |
| 4-11/16" Square x 1-1/4" Deep | 25.5 cu.in. | 11 |
| 4-11/16" Square x 1-1/2" Deep | 29.5 cu.in. | 13 |
| 4-11/16" Square x 2-1/8" Deep | 42 cu.in. | 18 |
| Octagon Box 1-1/2" Deep | 15.5 cu.in. | 6 |
| 4" Octagon Box 1-1/2" Deep | 15.5 cu.in. | 6 |
| Octagon Box 2-1/8" Deep | 21.5 cu.in. | 9 |
| Single Gang Device Box 2-3/4" Deep | 14 cu.in. | 6 |
| Single Gang Device Box 18 cu.in. | 18 cu.in. | 8 |
| Single Gang Device Box 3-1/2" Deep | 18 cu.in. | 8 |
*Theoretical maximum. Use our box fill calculator for actual installation capacity including devices and other fill factors.
Calculate Box Fill with 12 AWG
Enter your 12 AWG conductor count and other components for instant NEC compliance verification.
Open Box Fill Calculator12 AWG Conductor Volume Allowance
Per NEC Table 314.16(B), 12 AWG conductors require 2.25 cubic inches (36.9 mm³) of box volume each. This volume allowance applies to:
- Each conductor originating outside the box and terminating or splicing inside
- Conductors passing through without splice (counted once per conductor)
- Device fill calculations (based on largest conductor connected)
- Equipment grounding conductor fill (based on largest ground)
When to Use 12 AWG Wire
12 AWG conductors are rated for 20 amps and commonly used for 20-amp circuits, kitchen outlets, bathroom gfcis, garage circuits. Always verify conductor sizing meets circuit requirements per NEC Article 310.
Box Fill Calculation Example
For a receptacle installation with two 12/2 NM cables:
- 4 × 12 AWG conductors = 4 × 2.25 = 9.00 cu.in.
- 2 × grounds (count as 1) = 1 × 2.25 = 2.25 cu.in.
- Internal clamps = 1 × 2.25 = 2.25 cu.in.
- 1 × receptacle = 2 × 2.25 = 4.50 cu.in.
- Total: 18.00 cu.in. minimum box volume required
Recommended Box Sizes for 12 AWG
Based on typical installations, consider these box sizes for 12 AWG wiring:
- 4" Square × 1-1/2" (21 cu.in.) - Good for single device with 2 cables
- 4" Square × 2-1/8" (30.3 cu.in.) - Better for 3+ cables
- 4-11/16" Square × 2-1/8" (42 cu.in.) - Best for multiple devices