Workshop reference
Wire Gauge Reference Chart
Common American Wire Gauge diameters and approximate copper resistance.
| AWG | Diameter, inch | Diameter, mm | Copper resistance, Ω/1000 ft |
|---|---|---|---|
| 10 | 0.1019 | 2.588 | 0.999 |
| 12 | 0.0808 | 2.053 | 1.588 |
| 14 | 0.0641 | 1.628 | 2.525 |
| 16 | 0.0508 | 1.291 | 4.016 |
| 18 | 0.0403 | 1.024 | 6.385 |
| 20 | 0.0320 | 0.812 | 10.15 |
| 22 | 0.0253 | 0.644 | 16.14 |
| 24 | 0.0201 | 0.511 | 25.67 |
Allowable current depends on insulation, temperature, bundling, installation method, voltage drop, and applicable electrical rules. Diameter alone does not establish a safe ampacity.
Use the chart as a starting point
Reference values help compare sizes and plan a job. Product specifications, codes, tolerances, and the actual material still control the final choice.
Sage's guided lesson
Gauge numbers run backward on purpose
American Wire Gauge feels backward the first time you use it: bigger numbers mean thinner wire. This lesson explains why that is, how to actually use the diameter and resistance columns together, and where the numbering system came from in the first place.
Backward on purpose
Why smaller numbers mean thicker wire
American Wire Gauge counts the number of drawing passes it takes to pull a wire down to a given diameter, starting from thick stock. Fewer passes means a thicker wire and a lower gauge number. More passes means a thinner wire and a higher gauge number. Once you think of the number as a pass count instead of a size, the backward feeling mostly goes away.
Because thicker wire carries current with less resistance and less heat buildup, lower gauge numbers are used for higher current circuits, and higher gauge numbers are reserved for lighter loads like signal wiring or small electronics.
When in doubt, go thicker, meaning a lower gauge number. Undersized wire for the load is a real fire risk, while oversized wire mainly costs a bit more copper.
Diameter and resistance together
Using this chart with resistance and voltage drop
The resistance column tells you how much voltage a given wire loses over distance at a given current, which matters most on long runs. The diameter columns are mainly useful for confirming a wire will physically fit a terminal, lug, or conduit fill calculation.
Basic voltage drop idea
volt drop ≈ current × resistance per 1000 ft × (round trip length ÷ 1000)The Voltage Drop Calculator and Wire Size Calculator run this math directly from a target current and distance, which is faster than working from the resistance column by hand for a real circuit.
I know this is off topic, but this reminds me of a joke I heard when teaching this to one of my interns, Why did the shoe stay home from school? It wasn't feeling well-heeled. Yeah, I don’t see the connection either, but I think it is cute!
Before you wire it up
Tips and common mistakes
- Diameter alone does not set a safe current rating. Insulation type, ambient temperature, bundling with other conductors, and local electrical code all affect the real ampacity of a given gauge.
- Aluminum and copper wire of the same gauge do not carry the same current safely. Aluminum needs a larger gauge for an equivalent copper ampacity.
- Long wire runs lose more voltage even when the gauge is otherwise adequate for the current. Check voltage drop separately from basic ampacity on long circuits.
This chart is a reference for comparison and planning. Always confirm the final wire size and installation method against your local electrical code before wiring anything.
Where the numbering came from
A little history
American Wire Gauge grew out of 19th century wire manufacturing, where wire was pulled through a series of progressively smaller dies to reach a finished diameter. The gauge number reflected roughly how many drawing steps that took, which is why the scale runs the direction it does. As electrical wiring became standardized for telegraph, then telephone, then household power, this manufacturing scale carried over into the electrical trade rather than being replaced by a purpose-built system.
Other countries and industries developed their own wire gauge standards around the same era, which is part of why AWG is common in North America while metric wire cross-section, measured in square millimeters, is more common elsewhere.
Current events, handled
Class is over. It is officially cheese fries time.
You now know why AWG numbers run backward, and how to use the diameter and resistance columns together instead of picking a gauge by guesswork. That earns cheese fries, Sage's favorite way to celebrate a finished lesson.
Quick answers
Wire gauge questions
Why does a smaller AWG number mean a thicker wire?
AWG originally tracked how many drawing passes it took to pull wire down from thick stock. Fewer passes meant a thicker result and a lower gauge number, and that scale carried directly into modern electrical wiring.
Can I use this chart to pick a wire size for a circuit?
Use it as a starting comparison, then confirm the final size with the Wire Size Calculator and your local electrical code, since insulation type, temperature, and bundling all affect the real safe ampacity.
Does the same gauge carry the same current in copper and aluminum?
No. Aluminum has higher resistance than copper for the same size, so aluminum wiring needs a larger gauge to safely carry the same current as copper.
Why does resistance matter if the wire is rated for the current?
Resistance causes voltage drop over distance, which can leave equipment running below its rated voltage on long runs even when the wire is otherwise sized correctly for the current.