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AWG Wire Size Calculator

Pick an AWG size (4/0 through 40) and the tool instantly returns the wire diameter (mm / in), cross-sectional area (mm² / kcmil), DC resistance of copper or aluminium at 20 °C, and two standard ampacity references — single-conductor chassis wiring in free air, plus the US NEC 310.16 figure for three current-carrying copper conductors in a raceway at 60 °C.

Wire diameter

2.053 mm

0.0808 in

Cross-sectional area

3.31 mm²

6.53 kcmil

DC resistance (20 °C)

5.21 Ω/km

1.588 Ω / 1000 ft

Chassis / free-air ampacity

41 A

NEC 310.16 (60 °C Cu, 3-in-raceway)

20 A

Ampacity reference: free-air column from the PowerStream wire-gauge table (single insulated conductor in open air); NEC values from US NEC 310.16 (three current-carrying conductors in a raceway/cable, 60 °C insulation). Real-world sizing must also factor in insulation rating, ambient temperature, installation method and voltage drop.

Formula

d(n) [in] = 0.005 × 92^((36 − n)/39); A = π·d²/4; R/L [Ω/km] = (ρ/A) × 1000, with copper ρ = 1.724×10⁻⁸ Ω·m and aluminium ρ = 2.82×10⁻⁸ Ω·m

Frequently asked

Why does a larger AWG number mean a thinner wire?

The AWG system grew out of 19th-century American wire-drawing: the gauge number represents the number of passes through the drawing dies. Each extra pass squeezes the wire thinner, so a higher number means a finer wire. AWG 36 is anchored at 0.005 in (0.127 mm) and AWG 4/0 (0000) is anchored at 0.46 in. Everything in between is a geometric series connecting those two anchors, so adjacent gauges always differ in diameter by a fixed ratio of 92^(1/39).

Why are the chassis and NEC ampacity values so different?

The two columns describe different installations. Chassis / free air assumes a single insulated conductor in open air — typical for electronics enclosures or feeder leads in a panel, where heat dissipates easily. NEC 310.16 assumes three current-carrying conductors bundled in a raceway or cable, heating each other and surrounded by insulation, so the safe current is much lower for the same wire. Use NEC values for building-code-compliant wiring in the US/Canada; use chassis values for inside electronics, PCB pigtails or 12 V DC systems.

How does AWG map to metric mm² wire sizes?

There is no exact 1:1 mapping — the metric ladder (0.75 / 1.0 / 1.5 / 2.5 / 4 / 6 / 10 / 16 mm² …) is a different geometric series from AWG. Useful approximations: AWG 18 ≈ 0.82 mm², AWG 16 ≈ 1.3 mm², AWG 14 ≈ 2.1 mm² (≈ metric 2.5 mm²), AWG 12 ≈ 3.3 mm² (≈ metric 4 mm²), AWG 10 ≈ 5.3 mm² (≈ metric 6 mm²), AWG 8 ≈ 8.4 mm² (≈ metric 10 mm²). This calculator gives you the exact mm² figure so you can pick the closest metric size yourself.

What else matters besides ampacity when picking a wire size?

The most commonly forgotten factor is voltage drop. In low-voltage DC systems (12 V solar, automotive, drones) the cable run can be several metres, and a wire sized "just for ampacity" can drop 10–20 % of the voltage, hurting the load. A rule of thumb: cap voltage drop at 3 % (about 0.36 V on a 12 V bus). Use V = I × R together with the Ω/km figure this calculator gives you to back-compute the gauge you need. Other factors: insulation rating (PVC 60 °C vs THHN 90 °C), mechanical strength (go one size up where the wire flexes or is exposed), and frequency — skin effect raises the AC resistance above the DC figure for radio-frequency work.

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