Wire gauge conversion chart: AWG to MM2 explained

Wire gauge conversion trips people up because three sizing systems are in everyday use in UK workshops: AWG (American Wire Gauge) on imported components and US-authored schematics, metric mm² on European cable and anything specified to IEC standards, and the UK stranding convention (strands × strand diameter) that most hook-up wire is actually sold by. All three describe the same thing, the cross-sectional area of the conductor and a higher AWG number means a thinner wire: 20 AWG is 0.52 mm², 16 AWG is 1.31 mm².

This guide converts between all three systems, with resistance figures and practical selection advice for equipment builders, panel wirers and anyone specifying cables and wires for production or prototyping. One rule applies throughout: when substituting metric wire for an AWG size, always round up to the next standard metric size.

AWG to mm² conversion chart

The table below covers the AWG sizes most common in equipment wiring and electronics work. Conductor resistance is for annealed copper at 20°C; it rises with temperature, so treat it as a design baseline rather than a worst case. The nearest metric column shows the closest standard metric conductor size, where the fit is loose, size up.

Note: the nearest metric size is the closest standard conductor, not always a safe substitute. If a design calls for 18 AWG (0.823 mm²) and you're buying metric, 1.0 mm² keeps you on the right side of the specification; 0.75 mm² does not.

How do AWG sizes actually work?

AWG is a logarithmic scale that runs in the opposite direction to intuition: the number counts the drawing steps needed to reduce a copper rod to that diameter, so more steps means a thinner wire. That history gives the system two genuinely useful rules of thumb:

• Dropping three gauge numbers doubles the cross-sectional area and therefore halves the resistance per metre
• Dropping six gauge numbers doubles the diameter

This is why the resistance column in the chart above falls so predictably. If you know 20 AWG copper is about 33 mΩ per metre, you can estimate 23 AWG at roughly double that and 17 AWG at roughly half, without a table. For a stranded conductor of the same nominal size, expect resistance a few per cent higher than the solid figure, because the strands don't pack perfectly.

What do UK wire sizes like 7/0.2 mean?

Most general-purpose hook-up and equipment wire sold in the UK isn't labelled in AWG at all. The convention is strands / strand diameter in millimetres: 7/0.2 means seven strands of 0.2 mm wire, and multiplying the strand area by the count gives the conductor size. It's a system worth learning, because a schematic written in AWG and a UK supplier's catalogue are describing the same wire in two different languages. The table below is the translation.

*Typical figures for single-core PVC-insulated equipment wire in free air. Ratings vary between manufacturers and insulation types, confirm against the datasheet for the specific wire you're buying.

How much current can a wire gauge carry?

There is no single answer, and any chart that gives one without qualification is hiding assumptions. A conductor's safe current depends on how hot it's allowed to get, and that in turn depends on the insulation's temperature rating, whether the wire runs alone in free air or bundled inside a loom or trunking, and the ambient temperature around it. The same 0.5 mm² conductor might carry 3 A comfortably as a single run but need derating by a third or more when bundled with a dozen others inside an enclosure.

The practical approach is to treat gauge selection as a two-step check:

• Size for heat: use the manufacturer's rated current for the actual insulation and installation conditions, derating for bundling and high ambient
• Size for voltage drop: check the drop over the real cable length - in low-voltage DC work this usually turns out to be the stricter constraint

It's common to end up specifying a wire two sizes larger than the thermal rating alone would suggest, purely to keep the far end of the cable at a usable voltage. For fixed installations, harsh environments or anything carrying mains, specification is governed by the wiring regulations and the cable standard rather than a conversion chart - the mains and equipment cable and automotive cable ranges list the relevant ratings per product.

How do you calculate voltage drop?

Voltage drop follows Ohm's law: drop = current × resistance per metre × cable length × 2. The doubling matters and is the step people forget - current flows out along one conductor and back along the other, so a 5 m cable is a 10 m circuit.

A worked example shows why this dominates low-voltage design. Take a 5 m run of 24 AWG (84 mΩ/m) feeding a 2 A load: 2 × 0.084 × 10 = 1.68 V lost in the cable. On a 12 V system that's tolerable; on a 5 V supply it's catastrophic, a third of the voltage gone before the load sees it. Move up to 16/0.2 (0.5 mm²) and the drop falls to about 0.7 V; at 32/0.2 (1.0 mm²) it's roughly 0.35 V. Same load, same length, three very different outcomes.

What's the difference between AWG and SWG?

SWG (Standard Wire Gauge) is the older British system, and although it has largely given way to metric sizing, it survives in a few corners of the catalogue, notably resistance wire, fuse wire and some winding wire. The two scales look interchangeable but aren't: 20 SWG is 0.914 mm diameter while 20 AWG is 0.812 mm, and the discrepancy varies across the range. If a legacy drawing or an older component specification quotes SWG, convert to millimetres first rather than assuming the AWG figure of the same number.

Frequently asked questions

What is 18 AWG in mm²?

18 AWG has a cross-sectional area of 0.823 mm² and a diameter of 1.02 mm. The nearest standard metric conductor is 0.75 mm², but when substituting metric wire for an 18 AWG specification, choose 1.0 mm² so the replacement isn't undersized.

Is a higher AWG number thicker or thinner?

Thinner. AWG counts the number of drawing operations used to make the wire, so 30 AWG (0.25 mm) is much finer than 10 AWG (2.59 mm). Decreasing the gauge number by three doubles the conductor's cross-sectional area.

What size is 16/0.2 wire in AWG?

16/0.2 wire - sixteen strands of 0.2 mm - has a conductor area of 0.5 mm², which is closest to 20 AWG. It's the standard general-purpose equipment wire size in the UK, typically rated around 3 A.

Can I substitute metric wire for an AWG size?

Yes, provided you round up. Choose the next standard metric size at or above the AWG conductor's area, for example, 1.5 mm² in place of 16 AWG (1.31 mm²). Check that the insulation rating and temperature class also meet the original specification.

What's the difference between AWG and SWG?

They're separate systems with different diameters at the same number: 20 SWG is 0.914 mm while 20 AWG is 0.812 mm. SWG is the legacy British scale, now mostly seen on resistance wire, fuse wire and older drawings. Convert to millimetres before comparing.

Does stranded wire carry less current than solid wire?

For the same conductor area, the difference is marginal - stranded wire has slightly higher resistance because the strands don't pack perfectly. Stranded is preferred wherever the wire flexes or vibrates; solid core suits breadboards and fixed point-to-point links.

Find the right wire for the job

Once the wire is sized, the termination hardware needs to match the conductor: browse crimps, splices and terminals by wire size, with crimp tools and dies, wire strippers and heat shrink tubing to finish the job properly.