8 AWG Wire Box Fill
8 AWG conductors support 40-amp circuits for ranges and large appliances.
3
cu.in. per conductor
49.2
mm³ per conductor
40A
Max Ampacity
Common Applications
Box Capacity for 8 AWG
Maximum number of 8 AWG conductors that fit in common electrical boxes (conductors only, not accounting for devices, clamps, or grounds).
| Box Type | Volume | Max 8 AWG* |
|---|---|---|
| 4" Square x 1-1/4" Deep | 18 cu.in. | 6 |
| 4" Square x 1-1/2" Deep | 21 cu.in. | 7 |
| 4" Square x 2-1/8" Deep | 30.3 cu.in. | 10 |
| 4-11/16" Square x 1-1/4" Deep | 25.5 cu.in. | 8 |
| 4-11/16" Square x 1-1/2" Deep | 29.5 cu.in. | 9 |
| 4-11/16" Square x 2-1/8" Deep | 42 cu.in. | 14 |
| Octagon Box 1-1/2" Deep | 15.5 cu.in. | 5 |
| 4" Octagon Box 1-1/2" Deep | 15.5 cu.in. | 5 |
| Octagon Box 2-1/8" Deep | 21.5 cu.in. | 7 |
| Single Gang Device Box 2-3/4" Deep | 14 cu.in. | 4 |
| Single Gang Device Box 18 cu.in. | 18 cu.in. | 6 |
| Single Gang Device Box 3-1/2" Deep | 18 cu.in. | 6 |
*Theoretical maximum. Use our box fill calculator for actual installation capacity including devices and other fill factors.
Calculate Box Fill with 8 AWG
Enter your 8 AWG conductor count and other components for instant NEC compliance verification.
Open Box Fill Calculator8 AWG Conductor Volume Allowance
Per NEC Table 314.16(B), 8 AWG conductors require 3 cubic inches (49.2 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 8 AWG Wire
8 AWG conductors are rated for 40 amps and commonly used for 40-amp circuits, electric ranges, large ac units, hot tubs. Always verify conductor sizing meets circuit requirements per NEC Article 310.
Box Fill Calculation Example
For a receptacle installation with two 8/2 NM cables:
- 4 × 8 AWG conductors = 4 × 3 = 12.00 cu.in.
- 2 × grounds (count as 1) = 1 × 3 = 3 cu.in.
- Internal clamps = 1 × 3 = 3 cu.in.
- 1 × receptacle = 2 × 3 = 6.00 cu.in.
- Total: 24.00 cu.in. minimum box volume required
Recommended Box Sizes for 8 AWG
Based on typical installations, consider these box sizes for 8 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