A 20 gauge AWG copper conductor measures 0.8128 mm (0.0319 in) across, with a cross-sectional area of about 0.518 mm².
For the full breakdown, see our best 20 Gauge Copper Wire guide.
20 Gauge Copper Wire Dimensions
In AWG, 20 gauge copper runs 0.8128 mm across the bare conductor — 0.0319 inches, or roughly 31.9 mils.
- Bare diameter: 0.8128 mm (0.0319 in)
- Cross-sectional area: about 0.518 mm²
- Chart readings: some tables list 0.8118 mm and 0.031961 in
- DC resistance: about 33.31 Ω/km at 20°C, or 10.15 Ω per 1,000 ft
- Closest metric size: 0.5 mm² — near, not equal
Every figure traces to the AWG relationship, where diameter in inches equals 0.005 × 92^((36 − n) / 39), and multiplying by 25.4 gives millimeters. Plug in 20 and the result lands on 0.8128 mm. Hundredth-of-a-millimeter differences between charts come from rounding, not a different wire.
Resistance is where size stops being trivia. At 10.15 Ω per 1,000 ft, a 100-foot run of 20 AWG adds roughly 1 Ω — noticeable voltage loss on a 12 V circuit, and the usual reason long runs get bumped up a size.
One limit the charts skip: those numbers describe a bare, solid conductor. Stranding and insulation sit on top.
| Measurement | 20 AWG Copper Value | Why It Matters |
|---|---|---|
| Bare conductor diameter | 0.8128 mm (0.0319 in) | Terminal and ferrule fit |
| Cross-sectional area | About 0.518 mm² | Current capacity baseline |
| Conversion-chart reading | 0.8118 mm / 0.031961 in | Rounding differences between tables |
| Resistance at 20°C | About 33.31 Ω/km | Voltage drop on metric-length runs |
| Resistance per 1,000 ft | About 10.15 Ω | Voltage drop on US-length runs |
| Nearest metric equivalent | 0.5 mm² | Close match, not an exact swap |
| Ampacity range | Roughly 5 A to 11 A | Depends on insulation and installation |
How Does 20 AWG Compare With 0.5 mm² Metric Wire?
They look identical on a shelf and are not exact substitutes. The mismatch runs opposite to most assumptions: 20 AWG carries about 0.518 mm² of copper, so it is slightly larger than a 0.5 mm² metric wire.
The AWG wire gauge diameter chart from Engineering Toolbox lists inch and millimeter values side by side, useful when a datasheet quotes only one unit.
Why A 20 Gauge Label Doesn’t Always Mean AWG
Gauge systems disagree, so the same label can point at two different diameters. British Standard Wire Gauge (SWG) runs on its own scale, and 20 gauge SWG is not 0.8128 mm. US electrical and hobby wire is normally AWG, but imported spools and generic listings aren’t always consistent — confirm the standard on the packaging or spec sheet before ordering.
Solid versus stranded adds another layer: diameter tables refer to a bare solid conductor, while stranded 20 AWG holds the same total copper area in a bundle that measures a little wider. Insulation pushes finished outside diameter past both, so bend radius and connector fit should come from the product datasheet, not a gauge chart.
Ampacity is the most-missed piece. It depends on insulation type, installation, and local code, so diameter alone can’t settle it. Published tables show roughly 11 A for 20 AWG in one 75°C context and about 5 A in another — same copper, different conditions.
Three checks before ordering:
- Confirm the standard is AWG, not SWG or a regional equivalent.
- Compare the finished outside diameter, not just the copper size.
- Rate current from the insulation rating and installation method.
FAQs
What is 20 gauge wire used for?
Its small diameter suits low-current jobs: model railroad layouts, LED lighting runs, small electronics, sensor leads, and short control wiring. For heavy current over long distances, a larger gauge keeps voltage drop and heat down.
How many amps can 20 gauge copper wire handle?
There is no single number. Ampacity changes with insulation rating, airflow, bundling, and local code. One chart lists about 11 A for 20 AWG at 75°C; another lists around 5 A under different conditions. Treat the manufacturer’s insulation rating and local code as the authority.
Is stranded 20 gauge wire bigger than solid 20 gauge wire?
Slightly, yes. Diameter tables describe the bare solid conductor, so stranded 20 AWG packs the same copper area into a bundle that measures a bit wider overall. Insulation widens both. For connector fit and bend radius, use the finished outside diameter on the datasheet.
References & Sources
- Engineering Toolbox. “AWG Wire Gauge Chart.” Supports the 20 AWG diameter, area, and resistance figures used above.
