Quick Reference — 8 AWG
Common uses: Range/oven circuits, central AC, hot tub/spa wiring, subpanel feeders
Wire Properties
| AWG Size | 8 AWG |
| Diameter (inches) | 0.1285″ |
| Diameter (mm) | 3.264 mm |
| Cross-sectional area | 8.37 mm² (16510 circular mils) |
| Resistance — Copper | 0.628 Ω per 1000 ft @ 20°C |
| Resistance — Aluminum | 1.03 Ω per 1000 ft @ 20°C |
| Weight (copper) | ~50.0 lb per 1000 ft |
Ampacity (Current Carrying Capacity)
Per NEC Table 310.16 — Copper conductor, 3+ current-carrying conductors in raceway/cable:
| Insulation Rating | Ampacity |
|---|---|
| 60°C (TW, UF) | 40A |
| 75°C (THW, THWN, XHHW) | 50A |
| 90°C (THHN, XHHW-2) | 55A |
Note: Actual ampacity may be reduced by ambient temperature corrections and conduit fill derating factors per NEC 310.15.
Voltage Drop Example
For a 15A load on 8 AWG copper wire, 100 ft one-way run (120V circuit):
Wire resistance: 0.628 Ω/1000ft × 200ft (round trip) ÷ 1000 = 0.1256 Ω
Voltage drop: 15A × 0.1256 Ω = 1.88V
Percent drop: 1.88V ÷ 120V = 1.6%
NEC recommends ≤3% voltage drop for branch circuits, ≤5% total (feeder + branch).
Nearby Sizes for Comparison
| AWG | Dia (in) | Dia (mm) | Area (mm²) | Ω/1000ft Cu | Ampacity 75°C |
|---|---|---|---|---|---|
| 6 | 0.1620 | 4.115 | 13.3 | 0.395 | 65A |
| 8 | 0.1285 | 3.264 | 8.37 | 0.628 | 50A |
| 10 | 0.1019 | 2.588 | 5.26 | 0.999 | 35A |
⚠️ AWG Sizing Reminder
- In AWG, lower numbers = thicker wire. 4 AWG is much thicker than 14 AWG.
- Each 3-gauge decrease doubles the cross-sectional area (e.g., 11 AWG ≈ 2× the area of 14 AWG).
- Each 6-gauge decrease doubles the diameter.
- Always follow local electrical codes — NEC values are minimum requirements.
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