AWG Wire Gauge Calculator
Wire gauge conversion, NEC current rating, and voltage-drop sizing — copper & aluminum, metric & imperial.
A free reference calculator for wire-and-cable engineers. American Wire Gauge (AWG) is the standardized system for conductor diameter — a smaller AWG number means a thicker wire. Use the tools below to convert AWG to metric, look up NEC current rating (ampacity), or size a conductor to a voltage-drop limit.
Convert
Current rating
Size a wire
AWG wire size chart (diameter, area, resistance & ampacity)
Reference values for solid copper conductors. Diameter and area follow ASTM B258; resistance is DC at 20 °C; ampacity columns are NEC NFPA 70 Table 310.16 (≤3 conductors, 30 °C ambient).
| AWG | Ø mm | Ø in | Area mm² | kcmil | Ω/km (Cu) | 60 °C A | 75 °C A | 90 °C A |
|---|---|---|---|---|---|---|---|---|
| 4/0 | 11.684 | 0.4600 | 107.2193 | 211.60 | 0.16 | 195 | 230 | 260 |
| 3/0 | 10.405 | 0.4096 | 85.0288 | 167.81 | 0.20 | 165 | 200 | 225 |
| 2/0 | 9.266 | 0.3648 | 67.4309 | 133.08 | 0.26 | 145 | 175 | 195 |
| 1/0 | 8.251 | 0.3249 | 53.4751 | 105.53 | 0.32 | 125 | 150 | 170 |
| 1 | 7.348 | 0.2893 | 42.4077 | 83.69 | 0.41 | 110 | 130 | 145 |
| 2 | 6.544 | 0.2576 | 33.6308 | 66.37 | 0.51 | 95 | 115 | 130 |
| 3 | 5.827 | 0.2294 | 26.6705 | 52.63 | 0.65 | 85 | 100 | 110 |
| 4 | 5.189 | 0.2043 | 21.1506 | 41.74 | 0.82 | 70 | 85 | 95 |
| 5 | 4.621 | 0.1819 | 16.7732 | 33.10 | 1.03 | — | — | — |
| 6 | 4.115 | 0.1620 | 13.3018 | 26.25 | 1.30 | 55 | 65 | 75 |
| 7 | 3.665 | 0.1443 | 10.5488 | 20.82 | 1.63 | — | — | — |
| 8 | 3.264 | 0.1285 | 8.3656 | 16.51 | 2.06 | 40 | 50 | 55 |
| 9 | 2.906 | 0.1144 | 6.6342 | 13.09 | 2.60 | — | — | — |
| 10 | 2.588 | 0.1019 | 5.2612 | 10.38 | 3.28 | 30 | 35 | 40 |
| 11 | 2.305 | 0.0907 | 4.1723 | 8.23 | 4.13 | — | — | — |
| 12 | 2.053 | 0.0808 | 3.3088 | 6.53 | 5.21 | 20 | 25 | 30 |
| 13 | 1.828 | 0.0720 | 2.6240 | 5.18 | 6.57 | — | — | — |
| 14 | 1.628 | 0.0641 | 2.0809 | 4.11 | 8.28 | 15 | 20 | 25 |
| 15 | 1.450 | 0.0571 | 1.6502 | 3.26 | 10.45 | — | — | — |
| 16 | 1.291 | 0.0508 | 1.3087 | 2.58 | 13.17 | — | — | — |
| 17 | 1.150 | 0.0453 | 1.0378 | 2.05 | 16.61 | — | — | — |
| 18 | 1.024 | 0.0403 | 0.8230 | 1.62 | 20.95 | — | — | — |
| 19 | 0.912 | 0.0359 | 0.6527 | 1.29 | 26.41 | — | — | — |
| 20 | 0.812 | 0.0320 | 0.5176 | 1.02 | 33.31 | — | — | — |
| 21 | 0.723 | 0.0285 | 0.4105 | 0.81 | 42.00 | — | — | — |
| 22 | 0.644 | 0.0253 | 0.3255 | 0.64 | 52.96 | — | — | — |
| 23 | 0.573 | 0.0226 | 0.2582 | 0.51 | 66.78 | — | — | — |
| 24 | 0.511 | 0.0201 | 0.2047 | 0.40 | 84.21 | — | — | — |
| 25 | 0.455 | 0.0179 | 0.1624 | 0.32 | 106.18 | — | — | — |
| 26 | 0.405 | 0.0159 | 0.1288 | 0.25 | 133.90 | — | — | — |
| 27 | 0.361 | 0.0142 | 0.1021 | 0.20 | 168.84 | — | — | — |
| 28 | 0.321 | 0.0126 | 0.0810 | 0.16 | 212.90 | — | — | — |
| 29 | 0.286 | 0.0113 | 0.0642 | 0.13 | 268.47 | — | — | — |
| 30 | 0.255 | 0.0100 | 0.0509 | 0.10 | 338.53 | — | — | — |
| 31 | 0.227 | 0.0089 | 0.0404 | 0.08 | 426.88 | — | — | — |
| 32 | 0.202 | 0.0080 | 0.0320 | 0.06 | 538.28 | — | — | — |
| 33 | 0.180 | 0.0071 | 0.0254 | 0.05 | 678.76 | — | — | — |
| 34 | 0.160 | 0.0063 | 0.0201 | 0.04 | 855.91 | — | — | — |
| 35 | 0.143 | 0.0056 | 0.0160 | 0.03 | 1079.28 | — | — | — |
| 36 | 0.127 | 0.0050 | 0.0127 | 0.03 | 1360.94 | — | — | — |
| 37 | 0.113 | 0.0045 | 0.0100 | 0.02 | 1716.12 | — | — | — |
| 38 | 0.101 | 0.0040 | 0.0080 | 0.02 | 2163.98 | — | — | — |
| 39 | 0.090 | 0.0035 | 0.0063 | 0.01 | 2728.73 | — | — | — |
| 40 | 0.080 | 0.0031 | 0.0050 | 0.01 | 3440.87 | — | — | — |
How it works — formulas & references
d(mm) = 0.127 · 92^((36−n)/39)
Diameter and area (π/4·d²) follow ASTM B258. IEC 60228 defines the equivalent metric conductor classes.
R = ρ · L / A (ρ at 20 °C)
Resistance is DC at 20 °C — copper ρ=1.724×10⁻⁸ Ω·m, aluminum 2.826×10⁻⁸ Ω·m. For large conductors at 60 Hz, AC resistance is slightly higher due to skin effect. IEC 60228 defines equivalent metric conductor classes.
NEC 310.16 × ambient × bundling
NEC NFPA 70 Table 310.16, with 310.15(B) ambient and 310.15(C) bundling derating. IEC 60364-5-52 for metric installations.
- Allowed drop = 3 % × 12 V =
0.36 V - Allowed resistance = 0.36 V ÷ (2 × 15 A × 5 m) =
0.0024 Ω/m(k = 2 for DC round-trip) - Smallest gauge at or below that → 8 AWG (2.06 Ω/km = 0.00206 Ω/m); 10 AWG (3.28 Ω/km) is too thin
- Actual drop at 8 AWG = 2 × 15 × 0.00206 × 5 =
0.31 V (2.6 %)✓
Results are reference estimates — verify against the applicable code and the authority having jurisdiction (AHJ) for any installation.
Sources
- ASTM B258 — standard AWG dimensions
- NEC NFPA 70, Table 310.16 & 310.15 — ampacity & derating
- IEC 60228 — metric conductor classes
- IEC 60364-5-52 — current-carrying capacity & installation
Reviewed by
TeleWire Technology · ISO 9001:2015 certified cable-assembly manufacturer
Last reviewed June 2026
AWG vs SWG vs metric (mm²)
Three systems describe the same wire — and the same gauge number is a different diameter in each. Always confirm which standard a spec uses.
American Wire Gauge — the US standard, defined by formula. A lower number means a thicker wire.
British / Imperial Standard Wire Gauge — a legacy fixed table that runs thicker than AWG for the same number.
IEC 60228 — states the actual conductor cross-section, which ultimately sets the current capacity.
| Gauge # | AWG Ø mm | SWG Ø mm |
|---|---|---|
| 16 | 1.291 | 1.626 |
| 18 | 1.024 | 1.219 |
| 20 | 0.812 | 0.914 |
| 22 | 0.644 | 0.711 |
| 24 | 0.511 | 0.559 |
Same number, different wire — SWG runs thicker than AWG. See the AWG guide for the full background.
Stranded vs solid conductors
- Single solid conductor — smallest overall diameter
- Lower cost; easy to terminate by IDC or in PCB holes
- Best for permanent, static installations
- Stiffer — can fatigue and break if repeatedly flexed
- Many fine strands — ~1.1–1.3× larger overall diameter
- Same copper area & ampacity at the same AWG
- Highly flexible — survives bending & vibration
- Standard for cable assemblies, harnesses, robotics & drag-chain
Same AWG = same cross-section and current rating; stranded simply trades a slightly larger diameter for flexibility. It's specified as equivalent solid AWG plus a strand count — e.g. 22 AWG 7/30 = seven strands of 30 AWG.
Glossary
- Ampacity
- The maximum continuous current a conductor can carry without exceeding its temperature rating.
- Circular mil (cmil)
- Area of a circle 0.001 in (one mil) in diameter — a US unit for conductor cross-section. 1 kcmil = 1,000 cmil.
- Voltage drop
- The loss of voltage along a conductor due to its resistance (V = k·I·R·L); typically kept under 3 % on a branch circuit.
- Resistivity (ρ)
- A material's intrinsic opposition to current. Copper ≈ 1.724×10⁻⁸ Ω·m at 20 °C; aluminum ≈ 2.826×10⁻⁸.
- Skin effect
- At higher AC frequencies, current crowds toward the conductor surface, raising effective resistance above the DC value.
- Derating
- Reducing a conductor's rated ampacity for high ambient temperature or for bundling several current-carrying conductors together.
AWG calculator — FAQ
What is AWG?
American Wire Gauge (AWG) is the standard U.S. system for specifying solid round conductor diameter. A lower AWG number is a thicker wire — every 6 gauges roughly halves or doubles the cross-sectional area.
How do I convert AWG to mm²?
Compute the diameter with d(mm)=0.127·92^((36−n)/39), then area = π/4·d². For example, 12 AWG ≈ 2.05 mm diameter ≈ 3.31 mm². Use the Convert tab above for any gauge.
What is the ampacity of 12 AWG copper?
Per NEC Table 310.16, 12 AWG copper is rated 20 A at 60 °C, 25 A at 75 °C and 30 A at 90 °C insulation, before ambient and bundling derating.
Copper vs aluminum — how much bigger does aluminum need to be?
Aluminum has ~1.6× the resistivity of copper, so an aluminum conductor carries less current for the same gauge — typically you go up about two AWG sizes to match a copper conductor's ampacity.
How do I size wire for voltage drop?
Use the Size-a-wire tab: enter current, run length, system voltage and a maximum %-drop. It returns the thinnest standard AWG whose drop stays within your limit, using R=ρL/A round-trip.
آیا به این گیج در یک مجموعه کابل سفارشی نیاز دارید؟
پس از تعیین اندازه هادی، TeleWire Technology آن را به یک مجموعه کابل یا دسته سیم سفارشی مطابق با استاندارد IPC/WHMA-A-620 تبدیل میکند — از نمونه اولیه تا تولید انبوه، ساخت تایوان.
درخواست استعلام قیمت