What is AWG?
The American Wire Gauge (AWG) system is a standardized method for measuring wire diameter used in North America. Established in 1857, it provides a consistent way to specify wire sizes for electrical conductors.
The Counter-Intuitive AWG Scale
The AWG system works inversely—as the gauge number increases, the wire diameter decreases. This can be confusing for beginners but makes sense when you understand the system's origins.
Quick Reference:
- Smaller AWG number = Larger wire diameter = More current capacity
- Larger AWG number = Smaller wire diameter = Less current capacity
Historical Background
The AWG system originated from the manufacturing process of drawing wire. Wire was pulled through progressively smaller dies, with each pass given a gauge number. The more times wire was drawn (higher gauge number), the thinner it became.
Mathematical Formula
AWG sizes follow a geometric progression. The diameter of any AWG size can be calculated using:
Diameter (inches) = 0.005 × 92((36-AWG)/39)
This formula shows the exponential relationship between gauge number and diameter.
Key AWG Sizes and Applications
Common Residential Wire Sizes
- 18 AWG: Lamp cords, doorbells, thermostats (low voltage/current)
- 16 AWG: Extension cords, small appliances
- 14 AWG: Lighting circuits, standard outlets (15A max)
- 12 AWG: Kitchen outlets, bathroom circuits (20A max)
- 10 AWG: Electric water heaters, clothes dryers (30A)
- 8 AWG: Electric ranges, central air conditioning (40-50A)
- 6 AWG: Large appliances, sub-panels (55-60A)
Larger Sizes for Heavy Loads
- 4 AWG: Service entrance conductors, feeders (70-85A)
- 2 AWG: Main service panels (95-115A)
- 1/0 AWG: Large service entrances (150A)
- 2/0 AWG: 175-200A services
- 4/0 AWG: 200-230A commercial services
Understanding "Aught" Sizes
Wire sizes larger than 0 AWG are designated with zeros followed by "/0" (pronounced "aught"). These represent continuation of the scale beyond zero:
- 1/0 (one aught): Larger than 1 AWG
- 2/0 (two aught): Larger than 1/0
- 3/0 (three aught): Larger than 2/0
- 4/0 (four aught): Largest common AWG size
Beyond 4/0, wire is typically measured in thousands of circular mils (kcmil or MCM).
AWG Size Progression Rules
The 3-Gauge Rule
Every decrease of 3 gauge numbers approximately doubles the wire's cross-sectional area and current capacity:
- 14 AWG → 11 AWG ≈ 2× area
- 12 AWG → 9 AWG ≈ 2× area
- 10 AWG → 7 AWG ≈ 2× area
The 6-Gauge Rule
Every decrease of 6 gauge numbers approximately doubles the wire diameter:
- 18 AWG → 12 AWG ≈ 2× diameter
- 12 AWG → 6 AWG ≈ 2× diameter
The 10-Gauge Rule
Every increase of 10 gauge numbers decreases the wire diameter by approximately a factor of 10:
- 10 AWG ≈ 0.1 inches diameter
- 20 AWG ≈ 0.01 inches diameter
- 30 AWG ≈ 0.001 inches diameter
Metric Equivalents
While AWG is standard in North America, many other countries use metric measurements (mm²) for wire size. Here are common conversions:
| AWG | Diameter (mm) | Area (mm²) | Metric Equivalent |
|---|---|---|---|
| 14 AWG | 1.63 | 2.08 | 2.5 mm² |
| 12 AWG | 2.05 | 3.31 | 4.0 mm² |
| 10 AWG | 2.59 | 5.26 | 6.0 mm² |
| 8 AWG | 3.26 | 8.37 | 10 mm² |
Stranded vs Solid Wire
AWG measurements apply to the total cross-sectional area of the conductor, whether solid or stranded:
- Solid wire: Single conductor, stiffer, better for permanent installations
- Stranded wire: Multiple thin strands, more flexible, ideal for applications requiring movement
Both solid and stranded versions of the same AWG size have the same current-carrying capacity, though flexibility and installation requirements differ.
Practical Selection Tips
Choose Larger Wire When:
- Wire runs exceed 50 feet (voltage drop concerns)
- Installing in hot environments (attics, near heat sources)
- Multiple circuits share a conduit (heat buildup)
- Planning for future expansion
- Working with aluminum instead of copper
Verify Your Selection:
- Check ampacity tables for temperature rating
- Calculate voltage drop for long runs
- Confirm NEC compliance for application
- Match wire size to breaker rating
- Consider local code requirements
Common Misconceptions
Myth: "Thicker is always better"
While oversized wire won't cause electrical problems, it can:
- Be difficult to install in tight spaces
- Not fit properly in terminals
- Increase costs unnecessarily
- Require larger conduit
Myth: "AWG is only for solid wire"
AWG applies to both solid and stranded conductors. The gauge number represents total cross-sectional area regardless of conductor construction.
Tools and Resources
Use our Wire Gauge Calculator to determine the correct AWG size for your project, and check the AWG Reference Chart for complete specifications.
Conclusion
Understanding the AWG system is fundamental to electrical work. While the inverse numbering might seem confusing at first, the system provides a standardized, precise method for specifying wire sizes that has served North America well for over 160 years.