20 gauge wire measures 0.813 mm across. Its cross-section is 0.519 mm², or 1,020 circular mils.
Everywhere else on this site the advice is to round up. Here it is not.
Look at the two options
| Option | Cross-section | Against 20 AWG |
|---|---|---|
| 0.5 mm² | 0.5 mm² | 4% less |
| 20 AWG | 0.519 mm² | — |
| 0.75 mm² | 0.75 mm² | 45% more |
0.5 mm² is within 4%. 0.75 mm² is nearly half as much copper again.
That is the widest asymmetry anywhere in the range. At 14 AWG the choice is 20% up against 28% down and both are real. Here one option is a rounding error and the other is a different cable.
And the resistance test agrees
A 20 AWG conductor runs about 33.23 Ω/km.
| Metric size | Limit | Result |
|---|---|---|
| 0.75 mm² | 24.5 Ω/km | fails by 36% |
| 0.5 mm² | 36.0 Ω/km | passes |
20 AWG satisfies the 0.5 mm² requirement comfortably. It is nowhere near meeting 0.75 mm².
So both the arithmetic and the test point the same way: 0.5 mm² is the match. Rounding up here costs 45% more copper and buys nothing you needed.
This is the only gauge on the site where I would tell you to take the smaller metric size without qualification.
Why the pattern reverses here
Round-up is normally right because the metric series is finer than the AWG series in the middle of the range — the size above is usually 12 to 25% larger and the size below is 24 to 28% smaller.
At the bottom the metric series gets coarse. Below 1 mm² it runs 0.5, 0.75, 1 — three sizes covering the range where AWG has 18, 19, 20, 21, 22 and more. So the AWG conductor sometimes lands almost exactly on a metric size, as it does here, and the next size up is a long way off.
The same coarseness works against you one gauge down. 22 AWG has no metric size below it at all — 0.5 mm² is the floor of the standard, and 22 AWG sits 54% underneath it.
20 AWG is the last gauge with a usable match. More on the underlying mismatch in why AWG doesn’t match metric sizes.
Ampacity
20 AWG does not appear in the standard ampacity tables — they stop at 18 AWG. On the metric side the current-carrying capacity tables start at 1.5 mm², so 0.5 mm² is not listed either.
Neither omission is an oversight. This is a signal and control conductor, and where it carries current the rating comes from the equipment standard or the flexible cord rules rather than the general power tables.
Conductor diameter
0.813 mm is solid wire. At 0.5 mm²:
| Construction | Max diameter | Min strands | Max strand dia. |
|---|---|---|---|
| Class 1, solid | 0.9 mm | 1 | — |
| Class 2, stranded | 1.1 mm | 7 | — |
| Class 5, flexible | 1.1 mm | — | 0.21 mm |
| Class 6, very flexible | 1.1 mm | — | 0.16 mm |
Note that class 2, class 5 and class 6 all share the same 1.1 mm maximum at this size. What separates them is strand count and strand fineness, not overall diameter.
For anything that flexes in service, class 6 at 0.16 mm strands is what you want. See conductor classes 1, 2, 5 and 6.
Where 20 AWG is used
Instrumentation and control wiring, panel interconnects, low-current signal runs, alarm and security cable, and internal wiring in equipment.
It is light enough that termination method matters more than current. Push-in terminals, crimp contacts and ferrules all have a minimum they will hold reliably, and 20 AWG is around where that becomes a design consideration.
FAQ
How many mm is 20 gauge wire?
0.813 mm in diameter for solid wire, which is 32.0 mils. Stranded 20 AWG measures wider, up to about 1.1 mm.
What is 20 AWG in mm²?
0.519 mm². The metric size to use is 0.5 mm², which is only 4% smaller.
Is 20 AWG the same as 0.5 mm²?
Very nearly. 0.5 mm² is 4% smaller, and a 20 AWG conductor meets the 0.5 mm² resistance limit. For practical purposes they are interchangeable, which is unusual — most gauges are not.
Should I round up to 0.75 mm²?
Only if a specification demands it. 0.75 mm² is 45% more copper than 20 AWG needs, and 0.5 mm² already meets the requirement.
How many amps can 20 gauge wire carry?
It is not listed in the standard ampacity tables, which stop at 18 AWG. Where 20 AWG carries current the rating comes from the equipment standard or the flexible cord rules.
Is 20 gauge thicker than 22 gauge?
Yes. 20 AWG is 0.813 mm against 0.643 mm, and it has 60% more copper.
Reference
| Property | 20 AWG |
|---|---|
| Diameter, solid | 0.813 mm |
| Diameter, solid | 32.0 mils / 0.032 in |
| Cross-sectional area | 0.519 mm² |
| Area | 1,020 cmil |
| Resistance, solid copper at 20 °C | 33.23 Ω/km |
| Metric size to use | 0.5 mm² (−4%, and 20 AWG meets its limit) |
| Metric size above | 0.75 mm² (+45%) |
Convert any other gauge with the AWG to mm² converter, or work from 0.5 mm² to AWG.