The first time most people look at an AWG wire gauge chart, the numbering feels backwards: 14 AWG is thinner than 10 AWG, and 2 AWG is thicker than both. Once you know why the scale runs in reverse, the rest of the chart — diameter, circular mils, ampacity — falls into place quickly.
The American Wire Gauge system, also known as the Brown & Sharpe wire gauge, was established in 1857. It runs on an inverse scale: as the physical diameter of the wire increases, the gauge number decreases. A thick 2 AWG wire is physically much larger than a thin 14 AWG wire.
Reading the Ampacity Chart
Once you understand the numbering direction, the rest of the chart is a lookup table. Find your load current in the ampacity column that matches your terminal temperature rating (usually 75°C), then read across to the AWG size in the left column.
| AWG Size | 75°C Ampacity | Max Overcurrent Protection |
|---|---|---|
| 14 AWG | 20A | 15A |
| 12 AWG | 25A | 20A |
| 10 AWG | 35A | 30A |
| 8 AWG | 50A | 50A |
| 6 AWG | 65A | 60A |
Copper conductors, 75°C ampacity column. Notice the ampacity column and the max overcurrent protection column aren't always equal — that's NEC 240.4(D) capping small conductors, covered below.
Look Up Any Wire Size Instantly
See the full interactive AWG chart with diameter, area, and ampacity for copper and aluminum.
Worked Example: Matching Wire to a 20A, 100-Foot Run
Ampacity alone doesn't always tell the whole story. Take a 120V, 20A load with a 100-foot run: reading the ampacity chart alone, 12 AWG is rated for 25A at 75°C, comfortably above the 20A load. But at 100 feet, 12 AWG voltage drop runs over 5% — well past the usual 3% guideline. Stepping up to 10 AWG copper keeps voltage drop to about 3.2% over the same distance. The chart's ampacity column answers "will this wire overheat?" — it doesn't answer "will the load still get enough voltage at the far end?" Long runs need both checks.
Key Rules for Reading Any AWG Chart
- Smaller number = thicker wire. The scale is inverse; 4 AWG is thicker than 8 AWG, which is thicker than 12 AWG.
- Beyond 4/0, sizes switch to kcmil. After 1/0, 2/0, 3/0, and 4/0 ("four-aught"), the largest conductors are measured in thousand circular mils rather than continuing the AWG sequence.
- Match your terminal temperature rating. Most standard equipment terminals are rated 75°C — use that ampacity column even for 90°C-rated wire like THHN.
- Ampacity and breaker size aren't always the same number. NEC 240.4(D) caps the maximum overcurrent protection for small conductors — 14 AWG copper is capped at a 15A breaker and 12 AWG at 20A, even though their 75°C ampacity is higher.
- Ampacity isn't the only limit on long runs. Check voltage drop separately for runs over roughly 75-100 feet.
Frequently Asked Questions
Why does a smaller AWG number mean a thicker wire?
The American Wire Gauge system, established in 1857, is an inverse scale: it originally tracked how many drawing passes a wire needed to reach a given diameter, so a wire drawn down more times (thinner) got a higher number. As physical diameter increases, the gauge number decreases — a 2 AWG wire is physically much larger than a 14 AWG wire.
What comes after 4/0 AWG on the chart?
Sizing jumps to 1/0, 2/0, 3/0, and 4/0 (pronounced "four-aught") for extremely large conductors. Beyond 4/0, sizes are measured in kcmil (thousand circular mils) instead of continuing the AWG number sequence.
Which ampacity column on the chart should I use?
For most standard building installations, match your load to the 75°C ampacity column, since most residential and commercial equipment terminals are rated at 75°C — even when the wire itself, like THHN, is rated for 90°C.
What gauge wire for a 20 amp circuit?
For a standard 20 amp circuit, use 12 AWG copper wire. Although 12 AWG copper has a terminal rating of 25A at 75°C, NEC 240.4(D) restricts the maximum overcurrent protection (breaker) for 12 AWG to 20A.
Can I just pick the smallest wire that meets my amperage on the chart?
Ampacity is the starting point, but not the only factor. On long runs, voltage drop can require a larger gauge than ampacity alone would suggest — for example, a 120V, 20A load run 100 feet needs 10 AWG copper to keep voltage drop under 3%, even though 12 AWG is ampacity-rated for 20A on a short run.
Conclusion
Once the inverse numbering clicks, an AWG chart is just a lookup: pick your temperature-rated ampacity column, find a size that clears your load current, then double-check voltage drop if the run is long. The gauge number itself is really a proxy for cross-sectional area — smaller number, more copper, higher ampacity.
Disclaimer: While our articles and tools are designed to align with the National Electrical Code, always check with local building inspectors and licensed electrical contractors before initiating physical installations.