Wire Gauge Chart (AWG)
American Wire Gauge (AWG) is the standard for conductor sizes in North America. Smaller gauge numbers mean thicker wire. After 1 AWG the sizes continue as 1/0, 2/0, 3/0 and 4/0 ("one-aught" to "four-aught"), and above 4/0 conductors are sized in thousands of circular mils (kcmil), such as 250 kcmil.
AWG wire gauge chart (building wire, 14 AWG to 4/0)
| Gauge | Diameter (in) | Diameter (mm) | Circular mils | Area (mm²) | Cu ampacity 75°C |
|---|---|---|---|---|---|
| 14 AWG | 0.0641 in | 1.63 mm | 4,110 | 2.08 mm² | 20 |
| 12 AWG | 0.0808 in | 2.05 mm | 6,530 | 3.31 mm² | 25 |
| 10 AWG | 0.1019 in | 2.59 mm | 10,380 | 5.26 mm² | 35 |
| 8 AWG | 0.1285 in | 3.26 mm | 16,510 | 8.37 mm² | 50 |
| 6 AWG | 0.1620 in | 4.12 mm | 26,240 | 13.30 mm² | 65 |
| 4 AWG | 0.2043 in | 5.19 mm | 41,740 | 21.15 mm² | 85 |
| 3 AWG | 0.2294 in | 5.83 mm | 52,620 | 26.67 mm² | 100 |
| 2 AWG | 0.2576 in | 6.54 mm | 66,360 | 33.63 mm² | 115 |
| 1 AWG | 0.2893 in | 7.35 mm | 83,690 | 42.41 mm² | 130 |
| 1/0 AWG | 0.3249 in | 8.25 mm | 105,600 | 53.48 mm² | 150 |
| 2/0 AWG | 0.3648 in | 9.27 mm | 133,100 | 67.43 mm² | 175 |
| 3/0 AWG | 0.4096 in | 10.40 mm | 167,800 | 85.03 mm² | 200 |
| 4/0 AWG | 0.4600 in | 11.68 mm | 211,600 | 107.22 mm² | 230 |
Diameters are bare solid conductor, from the AWG definition d = 0.005 in × 92^((36−n)/39). Stranded conductors are slightly larger. Ampacity from NEC Table 310.16, 75°C column.
The ampacity column is the raw Table 310.16 value. It is not a breaker size: 240.4(D) still limits 14, 12 and 10 AWG copper to 15 A, 20 A and 30 A breakers, and NM-B cable is limited to the 60°C column. Size circuits from the ampacity chart.
Every three gauge steps roughly doubles the cross-sectional area (and halves the resistance). Every six steps roughly doubles the diameter. That is why 10 AWG has about twice the copper of 13 AWG and about twice the diameter of 16 AWG (0.1019 in vs. 0.0508 in). Two steps, such as 12 AWG to 10 AWG, add about 59% more area (10,380 ÷ 6,530 = 1.59), which is why stepping up one building-wire size cuts voltage drop by roughly a third.
Approximate resistance per 1,000 feet
| Gauge | Copper (Ω per 1,000 ft) | Aluminum (Ω per 1,000 ft) |
|---|---|---|
| 14 AWG | 3.14 | — |
| 12 AWG | 1.98 | 3.25 |
| 10 AWG | 1.24 | 2.04 |
| 8 AWG | 0.781 | 1.28 |
| 6 AWG | 0.492 | 0.808 |
| 4 AWG | 0.309 | 0.508 |
| 2 AWG | 0.194 | 0.319 |
| 1/0 AWG | 0.122 | 0.201 |
| 4/0 AWG | 0.061 | 0.100 |
Calculated as K × 1,000 ÷ circular mils, with K = 12.9 (copper) and 21.2 (aluminum) ohm-cmil/ft, the approximation used in the voltage drop calculator. NEC Chapter 9 Table 8 lists exact DC resistance at 75°C for solid and stranded conductors, and Table 9 gives AC values for larger feeders.
Example: a 120 V circuit on 12 AWG copper, 50 feet one way, carrying 16 A. The current travels 100 feet out and back, so resistance is 0.1 × 1.975 = 0.1975 Ω, and the drop is 0.1975 × 16 = 3.16 V, or 2.6%. Same answer as the voltage-drop formula 2 × K × I × L ÷ cmil.
How to tell what gauge a wire is
- Read the jacket or insulation. Building wire is printed with its size, type and voltage rating, for example "12 AWG THHN/THWN-2 600V". NM cable is marked on the outer jacket ("12-2 W/G").
- Check the jacket color on NM-B cable. In the US, manufacturers use a common color scheme: white for 14 AWG, yellow for 12 AWG, orange for 10 AWG, and black for 8 and 6 AWG. The color is a convention, not a code requirement, so confirm with the printing.
- Measure the bare conductor. Strip a short length and measure with calipers, or use a wire-stripper gauge. A solid 12 AWG conductor measures about 0.081 in (2.05 mm); 14 AWG is about 0.064 in (1.63 mm).
- Use a wire gauge tool. A round sheet-metal wire gauge with slots gives a fast read on solid conductors.
Stranded conductors have a slightly larger overall diameter than solid wire of the same gauge because of the air gaps between strands. Measure the strand bundle only as a rough check.
Common questions about sizes
- Is 12 gauge thicker than 14 gauge? Yes. Lower number = thicker wire.
- How thick is 12 gauge wire? About 0.081 in (2.05 mm) solid, 3.31 mm² cross-section.
- What does 12-2 mean on cable? Two insulated 12 AWG conductors (black and white) plus a bare ground. 12-3 adds a red conductor.
- What is 1/0 wire? The size one step larger than 1 AWG, about 0.325 in solid diameter. It's common for 125–150 A feeders.
Metric sizes vs. AWG
Wire outside North America is sold by cross-section in mm². Using the areas in the chart: 2.5 mm² falls between 14 AWG (2.08 mm²) and 12 AWG (3.31 mm²), 4 mm² between 12 AWG and 10 AWG (5.26 mm²), 6 mm² between 10 AWG and 8 AWG (8.37 mm²), and 10 mm² between 8 AWG and 6 AWG (13.30 mm²). There's no exact match, so never swap one for the other on paper; the NEC ampacity tables are written in AWG and kcmil, and cable used in a US installation should carry a US listing.
Solid vs. stranded
Branch-circuit wire from 14 to 10 AWG comes solid or stranded. From 8 AWG up, conductors installed in raceways must be stranded (310.3(C)), and stranded wire is easier to pull and bend. Stranded conductors need terminals rated for them; push-in (backstab) terminals on receptacles and switches typically accept solid wire only. Check the device instructions.
Common gauge mistakes
- Reading the NM-B jacket color as proof of size. Relabelled or old cable may not follow the convention.
- Measuring over the insulation. Gauge is the bare conductor; insulation thickness varies by type (THHN is thinner than XHHW-2).
- Treating aluminum and copper of the same gauge as equal. 10 AWG aluminum has about 64% more resistance than 10 AWG copper, and a lower ampacity.
- Assuming 1/0 is smaller than 1 AWG. The aught sizes get larger: 1/0 is bigger than 1, and 4/0 is the largest AWG size.
Gauge vs. ampacity
Gauge tells you the physical size. The current it may carry depends on the insulation temperature rating, the terminations, the wiring method and conditions such as ambient temperature and bundling. Use the ampacity chart or the wire size calculator for circuit sizing.
Frequently asked questions
What is the difference between AWG and kcmil?
AWG covers sizes up to 4/0. Larger conductors are named by their area in thousands of circular mils: 250 kcmil, 350 kcmil, 500 kcmil and so on.
What gauge is household wiring?
Mostly 14 AWG for 15 A lighting circuits and 12 AWG for 20 A receptacle circuits. Dryers typically use 10 AWG, and ranges 8 or 6 AWG depending on the wiring method.
What gauge wire do I need for 30 amps?
10 AWG copper or 8 AWG aluminum for a 30 A breaker. The full explanation, including dryer and water heater circuits, is on the 30 amp wire size page.
What gauge is thermostat wire?
Usually 18 AWG. Low-voltage wiring like this isn't sized by the building-wire ampacity tables.
Does AWG apply to speaker wire and extension cords?
Yes, the same gauge system is used, but ampacity for flexible cords comes from NEC Table 400.5(A)(1), not Table 310.16.
Related
Diameters calculated from the AWG definition; circular mils from NEC Chapter 9, Table 8; ampacity from Table 310.16. Last updated: October 6, 2026. Check results against the code edition and local amendments your jurisdiction enforces and with the AHJ; electrical work should be done by qualified people.