Wire Gauge Converter (AWG, SWG, mm²)
AWG and SWG to mm, mm², kcmil and the nearest metric size — with printable charts.
AWG chart
| AWG | in | mm | mm² | kcmil | Ω/km | Ω/1000 ft | kg/km |
|---|
About the Wire Gauge Converter (AWG, SWG, mm²)
Wire sizes come in three systems: American Wire Gauge (AWG) in North America, the old British Standard Wire Gauge (SWG) on older drawings and winding wire, and metric cross-sections in mm² (IEC 60228) almost everywhere else. This converter turns any of them — or a diameter in mm, inches or mils, or an area in mm², kcmil or circular mils — into all the others.
It also finds the nearest metric cable size and the next size up, and gives the DC resistance per km and per 1000 ft for copper or aluminium at any temperature, plus the weight of the bare conductor. Full AWG (0000–40) and SWG (7/0–50) charts are below the converter, ready to print or download.
How to use it
- In Convert from, choose what you have: an AWG or SWG gauge, a metric size, a diameter (mm, in or mil) or an area (mm², kcmil or circular mils).
- Pick the gauge or type the value. The diameter, area in every unit and the nearest AWG, SWG and metric sizes appear at once.
- Choose copper or aluminium and the temperature to see the resistance and weight per length.
- Scroll to the chart, choose AWG or SWG, and use Print chart or CSV for a reference copy. Your size is highlighted.
Examples
2.053 mm (0.0808 in) · 3.309 mm² · 6.53 kcmil · nearest metric 4 mm² · copper 5.211 Ω/km (1.588 Ω/1000 ft) at 20 °C
1.784 mm solid · gauge 13.2 → nearest 13 AWG; 14 AWG (2.08 mm²) is smaller, 12 AWG (3.31 mm²) larger
2.032 mm (0.080 in) · 3.243 mm² · nearest 12 AWG
126.7 mm² · 12.7 mm solid (500 mil) · nearest metric 120 mm², next size up 150 mm²
How AWG sizes work
ASTM B258 defines AWG by two fixed points — 36 AWG is 0.005 in and 0000 AWG is 0.4600 in — with 39 equal steps between them in a geometric series: d = 0.005 in × 92^((36 − n)/39), or 0.127 mm × 92^((36 − n)/39). The thick “aught” sizes use n = 0 for 0 (1/0), −1 for 00 (2/0), −2 for 000 (3/0) and −3 for 0000 (4/0).
Useful rules of thumb follow from the formula: each gauge step changes the diameter by about 12.3%; six steps halve the diameter; three steps halve the area; ten steps cut the area by about ten. Above 4/0, conductors are sized by area in kcmil (thousands of circular mils, formerly MCM): 250, 300, 350 kcmil and so on. One circular mil is the area of a circle 0.001 in across, 5.067 × 10⁻⁴ mm².
Standard Wire Gauge (SWG)
The Imperial Standard Wire Gauge was fixed by an Order in Council in 1883 and later given metric values in BS 3737:1964, a standard that has since been withdrawn. Unlike AWG it is a table, not a formula: 7/0 is 0.500 in, 14 SWG is 0.080 in (2.032 mm) and 50 SWG is 0.001 in. You still meet SWG on older drawings and for enamelled winding wire, where it is often given instead of a diameter in mm.
Metric sizes (IEC 60228)
Metric cables are named by a nominal cross-section — 1.5, 2.5, 4, 6, 10, 16, 25 mm² and up. IEC 60228 defines each size by its maximum resistance rather than an exact area, so a real conductor can have slightly less copper than its name suggests. There is no exact match between AWG and metric sizes: 12 AWG (3.31 mm²) sits between 2.5 and 4 mm², closer to 4. The next size up is the one to use when a metric cable replaces an AWG one by area — but always check current rating, voltage drop and terminal sizes too.
Resistance and weight
Resistance per length is ρ ÷ area, corrected for temperature with R_T = R₂₀ × (1 + α(T − 20)):
- Copper (IEC 60028, annealed): ρ₂₀ = 1/58 Ω·mm²/m = 0.017241, α = 0.00393 /K, density 8.89 g/cm³
- Aluminium (IEC 60889, hard-drawn): ρ₂₀ = 0.028264 Ω·mm²/m, α = 0.00403 /K, density 2.703 g/cm³
The weight is that of the bare metal (density × area: 1 mm² of copper weighs 8.89 kg per km). A rise from 20 °C to 75 °C increases copper’s resistance by 21.6%.
Sources
- ASTM B258, Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors
- Standard Wire Gauge: Order in Council; BS 3737:1964 (metric values, withdrawn)
- IEC 60028, International standard of resistance for copper; IEC 60889, Hard-drawn aluminium wire for overhead line conductors
- IEC 60228, Conductors of insulated cables
Limitations
- Diameters are for solid round wire. A stranded conductor of the same gauge or area is larger across, and a compacted one slightly smaller.
- Resistance is calculated from resistivity. Stranded, tinned and real-world conductors are allowed a little more; use the cable datasheet for exact values.
- Current ratings are deliberately not given: they depend on the insulation, how the cable is installed and the local wiring rules. Use the cable size calculator with your code’s table.
- These are wire gauges. Sheet-metal gauges (for steel, galvanised steel and aluminium sheet) use different tables.
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Frequently asked questions
What is 12 AWG in mm²?
3.31 mm² (2.053 mm diameter). The nearest metric cable size is 4 mm²; 2.5 mm² is smaller than 12 AWG.
Is 2.5 mm² the same as 14 AWG?
No. 14 AWG is 2.08 mm², so 2.5 mm² is about 20% larger — it falls between 14 AWG and 12 AWG (3.31 mm²), at roughly 13 AWG. Treat them as different sizes when checking current ratings.
What is the difference between AWG and SWG?
Both give smaller numbers to thicker wire, but the steps differ. AWG follows a formula (ASTM B258); SWG is a fixed British table from 1883. 14 SWG is 2.032 mm, while 14 AWG is 1.628 mm — the same number is not the same size.
What do kcmil and MCM mean?
Both mean thousands of circular mils. A circular mil is the area of a circle 0.001 in in diameter (5.067 × 10⁻⁴ mm²), so 250 kcmil is 126.7 mm². MCM is the older abbreviation.
How much does temperature change a wire’s resistance?
For copper, about 0.393% per °C: R_T = R₂₀ × (1 + 0.00393 × (T − 20)). 12 AWG copper is 5.211 Ω/km at 20 °C and 6.337 Ω/km at 75 °C. Set the temperature above the results to see it.