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AWG Wire Gauge Calculator

Convert AWG wire gauge to diameter (mm/inches), cross-sectional area (mm²), resistance per meter, and approximate current carrying capacity.

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Formula

din=0.005×9236−AWG39d_{in} = 0.005 \times 92^{\frac{36-AWG}{39}}
d— Wire diameter (in)
AWG— American Wire Gauge number
A— Cross-sectional area (π × (d/2)²) (mm²)
R— Resistance: ρ·L/A (copper ρ = 1/58 μΩ·m) (mΩ/m)

How It Works

This calculator converts AWG (American Wire Gauge) to diameter, cross-sectional area, and resistance for electrical engineers, installers, and designers working with copper and aluminum conductors. Per ASTM B258, AWG follows a logarithmic formula: diameter (inches) = 0.005 × 92^((36-AWG)/39), where AWG 36 = 0.005 inches and AWG 0000 = 0.46 inches. Each 3 AWG steps doubles cross-sectional area; each 6 AWG steps doubles diameter. Key values: AWG 10 = 2.588 mm diameter, 5.26 mm^2 area, 3.28 mohm/m resistance (copper at 20 C). Ampacity per NEC Table 310.16: AWG 14 = 15 A, AWG 12 = 20 A, AWG 10 = 30 A in 60 C-rated insulation. Resistance is critical: 100 ft of AWG 14 at 10 A drops 2.5 V (3.2% of 120 V), affecting motor starting and causing power waste.

Worked Example

Problem

A 50-foot run of AWG 12 copper wire supplies a 16 A load at 120 V. Calculate voltage drop, power loss, and verify NEC ampacity compliance.

Solution
  1. AWG 12 diameter: 0.005 × 92^((36-12)/39) = 0.0808 inches = 2.05 mm
  2. Cross-sectional area: pi × (2.05/2)^2 = 3.31 mm^2
  3. Resistance per ASTM B258: 5.21 mohm/m for copper at 20 C
  4. Total resistance: 5.21 mohm/m × 50 ft × 0.3048 m/ft × 2 (round trip) = 159 mohm
  5. Voltage drop: V = I × R = 16 A × 0.159 ohm = 2.54 V (2.1% of 120 V - acceptable per NEC 210.19)
  6. Power loss: P = I^2 × R = 256 × 0.159 = 40.7 W dissipated as heat
  7. NEC ampacity (60 C): AWG 12 = 20 A, load = 16 A (80% = compliant per NEC 210.20)

Practical Tips

  • ✓Quick ampacity (60 C copper, NEC 310.16): AWG 14 = 15 A, AWG 12 = 20 A, AWG 10 = 30 A, AWG 8 = 40 A, AWG 6 = 55 A. For 75 C/90 C insulation, increase by 15-25%. Derate 80% for continuous loads per NEC 210.20
  • ✓Voltage drop guideline per NEC 210.19: keep drops < 3% on branch circuits, < 5% total (feeder + branch). At 120 V, 3% = 3.6 V. Use voltage drop calculator or rule: V_drop = (2 × L × I × R)/1000 where R in mohm/ft
  • ✓Metric conversion per IEC 60228: AWG 12 = 3.31 mm^2, nearest IEC = 4 mm^2. AWG 10 = 5.26 mm^2, nearest IEC = 6 mm^2. Use IEC sizes for international projects

Common Mistakes

  • ✗Confusing AWG number direction - LOWER AWG = LARGER wire. AWG 10 is larger than AWG 14. This is counterintuitive but follows historical wire drawing standards (more draws = thinner wire = higher number)
  • ✗Not accounting for temperature effects per NEC - copper resistance increases 0.393%/C. AWG 12 at 75 C has 20% higher resistance than at 20 C. Ampacity tables are derated for elevated ambient
  • ✗Using copper ampacity for aluminum - aluminum has 61% conductivity of copper per ASTM. AWG 12 aluminum = AWG 10 copper for equivalent current. Always upsize aluminum 2 AWG steps

Frequently Asked Questions

American Wire Gauge, standardized in ASTM B258. Originally based on wire drawing: the number represents how many times a wire was drawn through dies from a standard stock. More draws = thinner wire = higher AWG number. AWG 0 (1/0) through 0000 (4/0) are larger than AWG 1.
Per NEC Table 310.16: larger wire (lower AWG) has higher ampacity due to lower resistance and better heat dissipation. Each 3 AWG steps doubles area and current capacity: AWG 12 = 20 A, AWG 9 = ~35 A, AWG 6 = 55 A (approximate). Actual ampacity depends on insulation temperature rating and installation conditions.
No - wire selection depends on current, voltage drop, temperature, and environment. Per NEC: power wiring uses ampacity tables; signal wiring considers impedance; automotive uses higher ampacity due to low voltage (12 V needs heavier wire to avoid significant percentage drop). Always verify against applicable code.

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