16 mm² converts to 5 AWG. Like several sizes in this range, that is the correct answer and not a useful one — 5 AWG is not stocked and it does not appear in the ampacity tables.
The decision you actually make is between 6 AWG and 4 AWG, and at this size those two are further apart in consequence than anywhere else in the common range.
A 31% gap between your two options
| Option | Cross-section | Against 16 mm² | Ampacity at 75 °C |
|---|---|---|---|
| 6 AWG | 13.3 mm² | −17% | 65 A |
| 5 AWG | 16.8 mm² | +5% | not tabulated |
| 4 AWG | 21.1 mm² | +32% | 85 A |
65 A against 85 A is a 31% span. On a 16 mm² design that is the difference between a circuit that carries the load and one that does not, and there is no intermediate option to reach for.
Compare that to smaller sizes, where the two candidates sit 20 to 25 A apart on a much lower base. Here the absolute gap is large enough to change the outcome.
The resistance test rules out 6 AWG
For 16 mm² the limit is 1.15 Ω/km for solid and stranded, 1.21 Ω/km for flexible.
| Gauge | Resistance | Result |
|---|---|---|
| 6 AWG | 1.30 Ω/km | fails by 13% |
| 5 AWG | 1.03 Ω/km | passes |
| 4 AWG | 0.82 Ω/km | passes |
6 AWG misses by 13% — the same margin that appears at 12 AWG against 4 mm² and 8 AWG against 10 mm². That repetition is not coincidence: both series step by a roughly constant ratio, so the mismatch recurs at similar magnitude up the range. See why AWG doesn’t match metric sizes.
So against a written specification, 4 AWG is the answer.
Why this size gets argued about
16 mm² is a common size for EV charge points, sub-mains, and larger single-phase supplies. Those are jobs where the cable is a visible cost and where someone will suggest 6 AWG on the grounds that it is close enough.
It is 17% less copper and it misses the resistance requirement. Whether that matters depends entirely on what the 16 mm² was sized for:
- Sized for current, with margin? 6 AWG at 65 A may clear the load. Run the calculation for the actual installation and record it.
- Sized for voltage drop on a long run? 6 AWG has 27% more resistance per metre than 5 AWG and 59% more than 4 AWG. That is exactly the wrong direction, and it is usually why 16 mm² was specified.
- Meeting a specification or a factory test? 4 AWG. No argument.
The 4 AWG overshoot of 32% is real money at this size, so the calculation is worth running properly rather than defaulting either way.
Ampacity
Three loaded conductors clipped direct at 30 °C:
| Insulation | 16 mm² | 6 AWG | 4 AWG |
|---|---|---|---|
| PVC / 70–75 °C | 76 A | 65 A | 85 A |
| XLPE / 90 °C | 96 A | 75 A | 95 A |
The XLPE row is worth a look. 4 AWG at 95 A and 16 mm² at 96 A are within one amp of each other, so on a 90 °C cable the two are effectively equivalent on current — the difference is the 32% of extra copper you paid for.
Derating still applies. 16 mm² XLPE in a 40 °C plant room with three circuits bunched:
96 A × 0.91 (40 °C) × 0.70 (3 circuits) = 61.2 AConductor diameter
A solid conductor of 16 mm² works out to 4.514 mm across. At this size the cable is stranded.
| Construction | Max diameter | Min strands | Max strand dia. |
|---|---|---|---|
| Class 1, solid | 4.6 mm | 1 | — |
| Class 2, stranded | 5.3 mm | 7 | — |
| Class 5, flexible | 6.3 mm | — | 0.41 mm |
| Class 6, very flexible | 6.3 mm | — | 0.21 mm |
Solid 6 AWG is 4.11 mm and solid 4 AWG is 5.19 mm.
Class 5 at 6.3 mm is 37% wider than the class 1 maximum. On EV charger installations in particular, where flexible cable is common and glands are ordered ahead of the cable, that is the number to size from. See conductor classes 1, 2, 5 and 6.
Where 16 mm² is used
EV charge point supplies, sub-mains, larger motor circuits, generator and inverter connections, and main earthing conductors on medium services.
FAQ
What is 16 mm² in AWG? 5 AWG by cross-sectional area, at 16.8 mm². 5 AWG is not commercially stocked and is absent from the ampacity tables, so the practical choice is 6 AWG or 4 AWG.
Can I use 6 AWG instead of 16 mm²? 6 AWG has 17% less copper, carries 65 A against 76 A, and misses the 16 mm² resistance limit by 13%. It may be acceptable on a circuit designed with margin. It is the wrong choice on a long run or against a specification.
Is 16 mm² the same as 4 AWG? No. 4 AWG is 21.1 mm², 32% larger. It is the nearest stocked gauge that is not smaller than 16 mm², which makes it the safe substitute.
Why is 5 AWG unavailable? Odd-numbered gauges are defined in the wire gauge standard but distributors carry even gauges and the 0-series. 5 AWG is also missing from the standard ampacity tables, so there is no published rating to design from.
What is 16 mm² in mm diameter? A solid conductor would be 4.514 mm across. Real 16 mm² cable is stranded and measures up to 5.3 mm, or 6.3 mm for flexible constructions.
Is 16 mm² enough for a 32 A EV charger? 16 mm² clipped direct is rated 76 A for PVC before derating, so a 32 A continuous load has room. Whether it remains adequate depends on the run length, the installation method, the ambient temperature, and the rules that govern EV supply circuits where you are working.
Reference
| Property | 16 mm² |
|---|---|
| Closest AWG by area | 5 AWG (16.8 mm², +5%) — not stocked |
| Commercial substitute | 4 AWG (21.1 mm², +32%) |
| Undersized option | 6 AWG (13.3 mm², −17%, fails the limit) |
| Equivalent solid diameter | 4.514 mm |
| Max resistance, class 1 and 2 | 1.15 Ω/km |
| Max resistance, class 5 and 6 | 1.21 Ω/km |
| Max conductor diameter | 4.6 / 5.3 / 6.3 mm by class |
| Ampacity, PVC clipped direct | 76 A before derating |
Work the other direction from 6 AWG or 4 AWG, or use the converter.