AWG Wire Size Chart: Complete Guide to American Wire Gauge

A single strand of 14 AWG copper has a resistance of about 2.525 ohms per thousand feet at 20 °C. Double the length to 2,000 feet and you have 5 ohms, enough to drop more than 10 volts off a 15 A circuit before the wire even reaches the load. That number is not arbitrary. It falls out of a formula set in Providence, Rhode Island in 1857, and every residential wire sold in North America today still obeys it.

American Wire Gauge (AWG), also called the Brown & Sharpe gauge, was standardized by the Brown & Sharpe Manufacturing Company in 1857. It replaced a patchwork of proprietary gauge systems that made cross-manufacturer wire selection essentially impossible. The system it defined is geometric, predictable, and, once you know the formula, lets you derive every diameter, area, and resistance value on the chart from scratch.

What AWG Actually Measures

AWG measures the diameter of round, solid, nonferrous electrical conductors. The gauge number itself is a step count on a geometric progression, not a linear measurement, which is why smaller numbers correspond to thicker wire. The heaviest standard size, 0000 AWG (written 4/0 and pronounced "four-aught"), is 0.4600 inches (11.684 mm) in diameter. The thinnest in the standard table, 40 AWG, is 0.00314 inches (0.0799 mm). The ratio between these two extreme diameters is exactly 1:92, spread across 39 steps from gauge 36 to gauge 0000.

Every AWG diameter can be computed from a single formula:

d(n) = 0.005 inch × 92^((36 − n) / 39)
     = 0.127 mm × 92^((36 − n) / 39)

For 0000 AWG, the exponent becomes n = −3 and you recover 0.4600 inches. For 36 AWG, the exponent is zero and d = 0.005 inches exactly. The choice of 92 as the diameter ratio was not an accident. It was picked so that a change of 3 gauge numbers roughly doubles the cross-sectional area, and a change of 10 gauge numbers increases diameter about tenfold by area (more precisely, a factor of 10.1). Both shortcuts are useful at the bench: drop three gauge numbers, get roughly twice the copper.

Cross-sectional area follows a parallel formula because area scales with the square of diameter:

A(n) = (π/4) × d(n)²
     ≈ 0.012668 mm² × 92^((36 − n) / 19.5)

In the US and Canada the old-school unit for wire cross-section is the circular mil. One circular mil is the area of a circle one mil (0.001 inch) in diameter, which works out to roughly 5.067 × 10⁻⁴ mm². For larger conductors, the chart uses kcmil (thousand circular mils), sometimes spelled MCM in older texts. A 250 kcmil conductor, for example, has a cross-section of 126.7 mm², larger than 4/0 AWG but smaller than the next wire-builder size up.

The Full AWG Table

Values for solid round copper at 20 °C. Diameter is rounded to 4 significant figures as the standard recommends. Ampacity column uses NEC 310.16 for 75 °C insulation (THWN, XHHW) in raceway, not free air. NEC 240.4(D) further limits the breakers for the smallest household sizes.

Numbers above 4/0 AWG are expressed directly in kcmil: 250 kcmil, 350 kcmil, 500 kcmil, and so on. There is no "5/0" in normal use.

AWG to Metric (mm²) Conversion

Outside North America, cable is specified directly in mm². There is no clean 1:1 AWG-to-mm² mapping because AWG steps do not align with the standardized IEC 60228 mm² series (1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120 mm²). The usual rule is to pick the nearest larger IEC size to stay safe on ampacity.

The common residential pairings are worth memorizing:

• 14 AWG ≈ 2.08 mm² (IEC equivalent: 2.5 mm²)
• 12 AWG ≈ 3.31 mm² (IEC equivalent: 4 mm²)
• 10 AWG ≈ 5.26 mm² (IEC equivalent: 6 mm²)
• 8 AWG ≈ 8.37 mm² (IEC equivalent: 10 mm²)
• 6 AWG ≈ 13.3 mm² (IEC equivalent: 16 mm²)
• 4 AWG ≈ 21.2 mm² (IEC equivalent: 25 mm²)
• 2 AWG ≈ 33.6 mm² (IEC equivalent: 35 mm²)
• 1/0 AWG ≈ 53.5 mm² (IEC equivalent: 50 mm², round up for 95 °C)
• 4/0 AWG ≈ 107.2 mm² (IEC equivalent: 95 or 120 mm²)

Stranded wire complicates things slightly. A stranded conductor has small air gaps between its strands, so its overall outside diameter is larger than a solid wire of the same AWG, even though the conductive cross-section is the same. When selecting conduit fill, use the stranded OD; when selecting for ampacity, use the AWG.

How to Pick Wire Gauge for a Real Project

Picking a gauge is usually a voltage-drop problem, not an ampacity problem. The NEC ampacity tables tell you how much current the wire can carry without overheating the insulation, but they do not guarantee the voltage at the load will be usable. For long runs, voltage drop governs.

Example: a detached garage subpanel, 150 feet from the main panel, fed at 240 V, expected steady load of 40 A.

Step 1. Check ampacity first. From the table above, 8 AWG copper at 75 °C is rated for 50 A. That clears 40 A with headroom, so 8 AWG is the ampacity floor.

Step 2. Compute voltage drop. Single-conductor resistance at 8 AWG is 0.6282 Ω/1000 ft. The current travels 150 feet out and 150 feet back, so total loop length is 300 feet. Loop resistance: 0.6282 × 300 / 1000 = 0.1885 Ω. At 40 A, voltage drop is 40 × 0.1885 = 7.54 V, which is 3.1 percent of 240 V. The NEC recommends keeping feeder drop under 3 percent and branch circuit drop under 3 percent as well, with a combined 5 percent ceiling. At 3.1 percent on the feeder alone, 8 AWG is already tight once you add the branch circuits downstream.

Step 3. Step up one trade size. 6 AWG has 0.3951 Ω/1000 ft. Loop resistance becomes 0.3951 × 300 / 1000 = 0.1185 Ω. Drop at 40 A is 4.74 V, or 1.98 percent. That leaves comfortable margin for the branch circuits inside the garage. 6 AWG is the correct answer.

Before trusting any rule of thumb, run the numbers through the wire size calculator and cross-check with the voltage drop calculator. For the underlying V = IR arithmetic, the Ohm's Law calculator is the fastest way to verify a single leg.

Common Residential Wire Sizes

North American house wiring leans heavily on five gauges. Knowing what each one is for is more useful than memorizing the whole table.

14 AWG is the standard for 15 A lighting circuits. The NEC allows 20 A raw ampacity on 75 °C copper, but 240.4(D) limits overcurrent protection to 15 A for general use, so the breaker is the constraint, not the wire. Typical uses: bedroom and living-room lighting, ceiling fans, smoke alarms.

12 AWG handles 20 A general-purpose receptacle circuits, including kitchen small-appliance branch circuits required by NEC 210.52(B). The ampacity is 25 A but the 240.4(D) rule holds it to 20 A. Many electricians default to 12 AWG for all receptacle runs because the difference in material cost is small and the voltage-drop margin is better.

10 AWG carries 30 A loads: electric clothes dryers (NEMA 14-30), most central air conditioners up to roughly 5 tons, and 240 V water heaters in smaller homes. On 75 °C copper the ampacity is 35 A, limited to 30 A by 240.4(D).

8 AWG is the go-to for 40 to 50 A circuits. Standard free-standing electric ranges are wired with 8 AWG to a NEMA 14-50 outlet. Level 2 EV chargers at 40 A also use 8 AWG, though 6 AWG is common when the run is long or the installer wants margin for future upgrades.

6 AWG serves 50 to 65 A circuits and is the usual size for a detached garage or workshop subpanel feed at moderate distances. It is also common for tankless electric water heaters and larger EV chargers.

4 AWG shows up at 85 A, typically for 100 A subpanel feeds and the service entrance of older small homes. Modern 200 A services use 4/0 aluminum or 2/0 copper for the service-entrance conductors.

Copper vs. Aluminum

Aluminum has about 61 percent the conductivity of copper by volume, which means an aluminum conductor needs a larger cross-section to carry the same current. The rule of thumb most electricians use is two gauge sizes up when switching from copper to aluminum, and the NEC tables bear this out: 2 AWG aluminum is rated 90 A at 75 °C, close to the 85 A rating of 4 AWG copper. Go one more step up and 1 AWG aluminum at 100 A clears copper's 3 AWG equivalent comfortably.

Another way to frame it: aluminum ampacity is roughly 78 percent of copper ampacity at the same gauge. An 8 AWG aluminum conductor is rated 40 A at 75 °C, versus 50 A for 8 AWG copper. Aluminum also has a higher thermal expansion coefficient than copper, which caused the connection failures that gave solid aluminum branch wiring a bad reputation in the 1970s. Modern aluminum service and feeder conductors use alloys (AA-8000 series) and antioxidant paste at terminations, which mitigates the problem, and aluminum remains standard for service-entrance cable and large feeders because it is significantly cheaper per amp delivered.

For branch circuits inside the home, copper is still the default. For service drops, meter-to-panel feeds, and long subpanel runs, aluminum is both common and code-compliant when sized correctly.

Where AWG Breaks Down

AWG covers a finite range. Above 4/0, conductors are sized in kcmil directly because the geometric progression produces unwieldy fractional gauge numbers. Below 40 AWG, wire becomes so fine that the standard recommends resolution tighter than 0.01 mils, and specialty applications (medical leads, magnet wire, microelectronics) use their own tables.

AWG also assumes DC or low-frequency AC resistance. At high frequencies, current concentrates near the outer surface of the conductor due to skin effect, and the effective resistance rises. For a solid copper wire at 60 Hz the skin effect is negligible up through about 4/0, but by a few MHz even 18 AWG has noticeably higher AC resistance than its DC value. Litz wire (many thin insulated strands woven together) exists specifically to defeat this in RF transformers and induction heating coils, and its AWG rating describes each individual strand rather than the bundle.

One more place AWG misleads: stranded wire with a large number of fine strands (welding cable, battery cable) is often sold by "flexible" AWG ratings that are not directly interchangeable with solid AWG at the same number. Always check the spec sheet for the actual cross-section in mm² or circular mils if you are mixing cable types on a single circuit.

Inside its design envelope, which is most of the electrical work done in North America, the 1857 formula still runs the table. Every number in the chart is just 92 raised to a simple fraction. Once you know that, the rest is arithmetic.