AWG wire gauge chart and converter

Introduction

American Wire Gauge (AWG) is the wire size system used in North America. The numbers run backwards: the higher the gauge, the thinner the wire. 12 AWG, the usual size for a 20 A household circuit, is 2.05 mm across and has a cross-section of 3.31 mm². Every six gauges halve the diameter, and every three gauges halve the area.

This calculator gives the diameter, area in mm² and circular mils, resistance and weight of any gauge from 4/0 to 40, in copper or aluminium, solid or stranded, at any temperature. It also works backwards from a measured diameter or a metric cross-section to the gauge, and shows the metric IEC size to use instead. The full chart is in the next section.

Formulas and AWG chart

ASTM B258 defines every gauge from two fixed points, 0000 at 0.4600 in and 36 at 0.0050 in, with 39 steps of equal ratio between them:

d = 0.005 in × 92^((36 − n) / 39)
A = π × d² / 4
area in circular mils = (d in mils)²

Resistance and weight per unit length:

R' = ρ20 × (1 + α (T − 20)) / A × k_s
m' = ρ_m × A × k_s

• n — gauge number; 0 (1/0) is 0, 00 (2/0) is −1, 000 (3/0) is −2 and 0000 (4/0) is −3
• ρ20 — resistivity at 20 °C: copper 1.7241 × 10⁻⁸ Ω·m, aluminium 2.8264 × 10⁻⁸ Ω·m
• α — temperature coefficient: copper 0.00393 /K, aluminium 0.00403 /K
• k_s — 1.02 for concentric stranded conductors (ASTM B8), 1 for solid wire
• ρ_m — mass density: copper 8 890 kg/m³, aluminium 2 705 kg/m³

AWG chart

Solid copper at 20 °C, from the formulas above. For stranded wire add 2 % to the resistance; for aluminium multiply the copper resistance by 1.64. The last column is the smallest IEC metric size with at least the same area.

Assumptions and limitations

• Diameters are those of solid round wire. A stranded conductor of the same gauge has the same metal area but a larger overall diameter, so measure stranded wire by its strand count and strand gauge, not by its outside diameter.
• Resistance is the DC value from ρ/A. Tinned copper, coated wire and real manufacturing tolerances give values a few percent higher.
• The metric size is the smallest IEC 60228 size at least as large in area. IEC conductors are specified by maximum resistance, so a 4 mm² conductor can carry slightly less copper than 4.00 mm².
• This page does not give the allowed current. Ampacity depends on the insulation rating, installation, bundling and ambient temperature, and is set by the wiring code: NEC Table 310.16 in the US, IEC 60364-5-52 elsewhere. Use the wire size calculator for the voltage drop.

Worked example

What are the size and resistance of 12 AWG solid copper wire at 20 °C, and which metric cable replaces it?

1. Gauge number n = 12, so d = 0.005 × 92^(24 / 39) = 0.0808 in = 2.053 mm.
2. Area: A = π × 2.053² / 4 = 3.309 mm², or 80.8² = 6 530 circular mils.
3. Resistance at 20 °C: R' = 1.7241 × 10⁻⁸ / 3.309 × 10⁻⁶ = 5.211 × 10⁻³ Ω/m = 5.211 Ω/km, which is 1.588 Ω/1000 ft.
4. Weight: 8 890 × 3.309 × 10⁻⁶ = 0.0294 kg/m, or 19.8 lb per 1 000 ft.
5. The smallest IEC 60228 size with at least 3.309 mm² is 4 mm².

So 12 AWG copper is 2.05 mm thick with 3.31 mm² of copper, and 4 mm² is its metric replacement; 2.5 mm² would have 24 % less copper.

FAQ

Related calculators

• Wire size by voltage drop — the smallest AWG and metric size for a circuit.
• Cable sizing and voltage drop — IEC cable selection with reactance and power factor.
• Ohm's law — voltage, current, resistance and power.
• Unit converter — kcmil, mm², inches and more.