AWG Wire Gauge Chart: Ampacity and Resistance
American Wire Gauge numbers run backwards: the smaller the number, the thicker the wire. Behind each gauge sits a circular-mil area that fixes its resistance and, with the NEC tables, its ampacity.
Reading the gauge: smaller number, bigger wire
American Wire Gauge (AWG) is the standard for round conductors in North America, and its most confusing feature is that the numbering is inverted. 14 AWG is thin, 6 AWG is fat, and 4/0 is enormous. Each step down in gauge number is a step up in cross-section. The scale comes from the old wire-drawing process: a wire was pulled through successive dies, and the gauge counted the number of draws, so more draws meant a thinner wire and a higher number.
Below 1 AWG the scale continues as 1/0, 2/0, 3/0 and 4/0 (spoken “one-aught” through “four-aught”), each larger than the last. Above that, conductors are sized directly in thousands of circular mils (kcmil).
Circular mils: the number that matters
The real quantity behind a gauge is its circular-mil (cmil) area. One circular mil is the area of a circle one mil (0.001 inch) in diameter. It is a convenient unit because the area in circular mils equals the diameter in mils squared — no need to carry π around. The cmil values for common gauges are 14 AWG = 4,107, 12 AWG = 6,530, 10 AWG = 10,380, 8 AWG = 16,510, 6 AWG = 26,240, 4 AWG = 41,740, 2 AWG = 66,360, 1/0 = 105,600 and 4/0 = 211,600. Notice the pattern: every three gauges roughly doubles the area, and every six gauges roughly doubles the diameter.
Circular mils drive everything else. Resistance is inversely proportional to cmil, and the voltage-drop formula puts CM right in the denominator. The AWG wire size chart lists cmil, resistance and ampacity together.
Resistance per 1,000 feet
Each gauge has a characteristic resistance. For copper at 75°C the NEC Chapter 9 Table 8 values (ohms per 1,000 ft) are 14 AWG = 3.07, 12 AWG = 1.93, 10 AWG = 1.21, 8 AWG = 0.764, 6 AWG = 0.491, 4 AWG = 0.308 and 2 AWG = 0.194. Aluminum is about 1.6 times higher for the same gauge. To get the resistance of a run, multiply by the length: 100 ft of 12 AWG copper is 1.93 × 100 / 1,000 = 0.193 ohm one-way. The Wire Resistance calculator does this for any gauge, length and metal.
Ampacity: how much current a gauge carries
Ampacity is set by the NEC, not by the geometry alone, because it depends on the insulation temperature rating and the installation. For 75°C copper the NEC 310.16 figures are 20 A for 14 AWG, 25 A for 12 AWG, 35 A for 10 AWG, 50 A for 8 AWG, 65 A for 6 AWG, 85 A for 4 AWG and 115 A for 2 AWG. Two cautions apply. First, the small-conductor overcurrent rule (240.4(D)) caps breakers at 15 A on 14 AWG, 20 A on 12 AWG and 30 A on 10 AWG even though the table is higher. Second, ampacity is derated for heat and bundling. Use the Ampacity calculator to apply the factors.
What size do I actually need?
The chart tells you what each gauge can do; choosing one means matching it to a load and a distance. Find the gauge that meets the derated ampacity for your current, then check that it holds voltage drop under your target over the run length, and take the larger of the two. A classic result: a 20 A load 100 feet away at 120 V needs 8 AWG for voltage drop even though 12 AWG would satisfy ampacity. The Wire Size calculator and the guide on sizing wire for amps and distance walk through the full method.
Common gauges at a glance
- 14 AWG — 15 A lighting and receptacle circuits.
- 12 AWG — 20 A general-purpose and kitchen circuits.
- 10 AWG — 30 A water heaters, dryers (with neutral), AC.
- 8 AWG — 40–50 A ranges and longer 20–30 A runs where voltage drop rules.
- 6 AWG and larger — subpanels, large appliances and feeders.
Solid versus stranded
The same gauge comes as solid and as stranded wire, and the distinction is worth understanding. Solid conductor is a single wire; stranded is many fine wires bundled to the same total cross-section. Because gauge is defined by the total copper area, a solid and a stranded conductor of the same AWG have essentially the same resistance and ampacity. What changes is handling: stranded is far more flexible and tolerates repeated bending, which is why it dominates in panels, vehicles and anywhere conductors flex, while solid is common in branch wiring where it holds its shape in a box. When you read a gauge off a chart, the electrical numbers apply to both forms; only the mechanical behavior and the termination style differ.
Why the chart is the same forever
One of the quiet virtues of an AWG chart is that it never goes out of date. Circular mils are pure geometry, and the resistance of copper and aluminum at a given temperature is a physical constant measured to high precision long ago. The only column that references a code edition is ampacity, and even there the underlying physics is stable; the values move only when the code committees adjust the conservative margins, and the changes are small. This is why a wire chart printed decades ago still gives correct geometry and resistance today. It is the canonical example of a reference table that needs no maintenance, which is exactly why it makes such a dependable foundation for the calculators built on top of it.
From the chart to a real circuit
A chart lists capability; a circuit needs a decision. To translate the table into an installed conductor, pair each load with the gauge whose derated ampacity covers it, then verify that the same gauge holds voltage drop under your target over the run length, and finally take the larger of the two. The table makes this easy because the three columns you need, circular mils, resistance and ampacity, sit side by side. Reading across a single row tells you at once how a gauge behaves electrically, while reading down a column shows how doubling the cross-section every three sizes steadily improves both resistance and current capacity.
Beyond 4/0: kcmil conductors
The AWG scale runs out at 4/0, which is about two hundred eleven thousand circular mils. Larger conductors, used for service entrances and big feeders, are sized directly in thousands of circular mils, written kcmil. A two hundred fifty kcmil conductor is simply two hundred fifty thousand circular mils of copper or aluminum, larger than 4/0. The same principles carry over: more circular mils mean lower resistance and higher ampacity, derated for heat and bundling exactly as with the smaller gauges. Most residential and off-grid work stays within the AWG range, but knowing that the scale continues smoothly into kcmil keeps the larger feeders from seeming mysterious.
The AWG figures are stable engineering constants. The ampacity values reference a specific NEC edition; confirm the one adopted by your jurisdiction and verify any sizing with a licensed electrician.