AWG (American Wire Gauge) is a size scale for round conductors where a smaller number means a thicker wire, and ampacity is the current a wire can carry without overheating — set not just by the gauge but by the insulation temperature rating, the ambient, and how many conductors are bundled together. That is why the same 6 AWG copper wire can be rated around 65 A as building wiring and around 101 A as a single conductor in free air. A size-and-ampacity chart is the starting point for choosing a harness conductor; the final size comes from the current, the voltage drop over the run, and the temperature the wire will see. This guide gives you the chart and how to use it.
TL;DR
- Lower AWG number = thicker wire. Every 3 gauges roughly doubles the cross-sectional area and halves the resistance.
- Ampacity depends on gauge and insulation temperature rating, ambient temperature, and bundling — not on gauge alone.
- 6 AWG copper: about 65 A as insulated building wiring (NEC 310.16, 75 °C), up to about 101 A as a single conductor in free air.
- Size a conductor for the real current, then check voltage drop over the length, then derate for temperature and bundle count.
- The chart values are a reference — confirm against the applicable code and the wire datasheet before releasing a design.
What AWG actually measures
AWG is a geometric scale: the gauge number counts drawing steps, so as the number goes up the wire gets thinner, and as it goes down the wire gets thicker. The relationship is regular — a drop of three gauge numbers (for example 10 AWG to 7 AWG) roughly doubles the cross-sectional area and halves the DC resistance, and a drop of ten gauges (10 AWG to 1/0-ish) is about a ten-fold area change. Above the largest single-digit gauges the scale continues as 1/0, 2/0, and so on for heavy conductors. Because the scale is about the copper cross-section, it is the copper area — not the outside diameter of the insulated wire — that sets resistance and current capacity.
Copper wire size chart (AWG)
These are the standard dimensions for solid copper. Stranded wire of the same AWG has the same nominal copper area but a slightly larger overall diameter and marginally higher resistance; the trade-offs are in our stranded vs. solid wire guide.
| AWG | Diameter (mm) | Area (mm²) | Copper resistance (Ω/km, 20 °C) |
|---|---|---|---|
| 24 | 0.511 | 0.205 | 84.2 |
| 22 | 0.644 | 0.326 | 52.9 |
| 20 | 0.812 | 0.518 | 33.3 |
| 18 | 1.024 | 0.823 | 20.9 |
| 16 | 1.291 | 1.31 | 13.2 |
| 14 | 1.628 | 2.08 | 8.28 |
| 12 | 2.053 | 3.31 | 5.21 |
| 10 | 2.588 | 5.26 | 3.28 |
| 8 | 3.264 | 8.37 | 2.06 |
| 6 | 4.115 | 13.3 | 1.30 |
| 4 | 5.189 | 21.2 | 0.815 |
| 2 | 6.544 | 33.6 | 0.513 |
Ampacity chart — and why one gauge has two numbers
Ampacity is where wire sizing gets misread, because a single gauge has very different ratings depending on how it is installed. A conductor run as a lone wire in open air sheds heat freely and carries more current; the same conductor bundled with others, or in conduit, runs hotter for the same current and must be derated. The two columns below show that spread: a single conductor in free air (the "chassis wiring" convention) versus insulated conductors sized as power wiring per NEC 2023 Table 310.16 at the 75 °C column. Read them as the outer bounds, not as a single answer.
| AWG (copper) | Single conductor in free air (≈A) | Insulated / bundled reference (≈A) |
|---|---|---|
| 24 | 3.5 | 2.1 |
| 22 | 7 | 3 |
| 20 | 11 | 5 |
| 18 | 16 | 7 |
| 16 | 22 | 10 |
| 14 | 32 | 20 |
| 12 | 41 | 25 |
| 10 | 55 | 35 |
| 8 | 73 | 50 |
| 6 | 101 | 65 |
| 4 | 135 | 85 |
| 2 | 181 | 115 |
Two cautions come with any ampacity table. First, small conductors used as branch-circuit wiring are further limited by overcurrent-protection rules — NEC 240.4(D), for example, caps the breaker on 14, 12, and 10 AWG regardless of the raw ampacity. Second, the free-air and NEC columns assume specific conditions; a harness inside a hot enclosure or a thick bundle sits between and below them once derated.
6 AWG ampacity, in context
Because "6 AWG wire ampacity" is one of the most searched sizes, it is a good example of the spread. A 6 AWG copper conductor is rated about 65 A as insulated building wiring at the 75 °C column of NEC 310.16 (55 A at 60 °C, 75 A at 90 °C), and up to about 101 A as a single conductor in free air. Neither is "the" answer — the usable figure depends on the insulation temperature rating, the ambient, and whether the conductor is bundled. For a battery or power lead inside a warm assembly, size from the derated value, not the free-air one.
How to size a harness conductor
A chart gives capacity; a correct size comes from three checks in order:
- Current. Start from the continuous current the circuit carries, with margin for inrush or fault where relevant, and read the gauge whose derated ampacity covers it.
- Voltage drop. Over a long run, resistance can force a larger conductor than ampacity alone would — use the Ω/km figure above to check the drop against the circuit's budget. Low-voltage DC systems are especially sensitive.
- Temperature and bundling. Derate for the ambient the harness sees and for the number of current-carrying conductors bundled together. The insulation temperature rating and derating factors are covered in our wire harness thermal management guide.
The insulation and jacket also decide what a gauge can do in a given environment; material selection sits in our wiring harness materials guide.
Representative project (anonymized)
Challenge. A United States smart-energy OEM needed a 2 AWG, 3-conductor power cable for home electrification, and the gauge was fixed by the current — but the assembly also had to meet the mandatory TYPE TC-ER certification on both the inner and outer jacket, and an initial jacket material substitution was rejected for failing that requirement. Approach. Working directly with the raw-cable manufacturer, an inner- and outer-jacket material combination was engineered to meet TC-ER while holding the target diameter and flexibility. Result. The compliant 2 AWG, 3-conductor specification was approved by the customer's mechanical engineering team and cleared the program toward high-volume production. The full write-up is in our TC-ER energy cable case study — a reminder that gauge sets the ampacity, but the insulation and certification decide whether that gauge is usable in the application.
AWG and ampacity FAQs
What is the ampacity of 6 AWG wire?
About 65 A for insulated copper at the 75 °C column of NEC 310.16 (55 A at 60 °C, 75 A at 90 °C), and up to about 101 A for a single conductor in free air. The usable figure depends on the insulation temperature rating, the ambient temperature, and whether the wire is bundled — always confirm against the applicable code and the wire datasheet.
Does a smaller AWG number mean a thicker wire?
Yes. AWG is inverse: the smaller the number, the larger the conductor. 6 AWG is much thicker than 24 AWG. Every three gauges of decrease roughly doubles the copper area and halves the resistance.
Why do ampacity charts disagree with each other?
Because they assume different installation conditions. A single conductor in free air carries far more than the same wire bundled or in conduit, and building-wiring tables add overcurrent-protection limits. A chart is only valid for the condition it was built for, which is why a harness value must be derated for its real ambient and bundle.
Do stranded and solid wire of the same AWG carry the same current?
Their nominal copper area and ampacity are the same for a given AWG, but stranded wire has a slightly larger overall diameter and marginally higher resistance, and it is the standard for anything that flexes. The selection trade-offs are in our stranded vs. solid wire guide.
