What AWG actually means

When to use this: choosing hookup wire for a project, checking whether an existing cable can carry a load, converting between AWG and metric sizes for sourcing, or working out how much voltage a long run will eat.

American Wire Gauge is defined by a formula, not a table. The diameter of gauge n in millimetres is:

d = 0.127 × 92^((36 − n)/39)

The two anchor points are 36 AWG at 0.127 mm and 0000 (4/0) at 11.68 mm, with 39 steps between them spaced geometrically. Everything else follows from that.

The scale runs backwards — a bigger number means a thinner wire. The number originally counted how many times the wire was drawn through a die to reach size, so more passes meant thinner wire. Conductors too thick for a single pass got the 0, 00, 000 and 0000 designations, written 1/0 through 4/0 and pronounced "one aught" through "four aught".

The useful shortcuts

• 6 gauges halves the diameter and quarters the cross-section.
• 3 gauges halves the area. So 10 AWG has twice the copper of 13 AWG.
• 10 gauges is a factor of 10 in area. 10 AWG has about ten times the copper of 20 AWG.

Ampacity: the number that depends on everything else

How much current a wire can carry is not a property of the wire. It is a property of the wire, its insulation, its surroundings and how fast heat can escape. The same 12 AWG copper conductor is rated:

That is a factor of two between the free-air figure quoted in electronics tables and the installation figure an electrician uses. Both are correct for their context, and confusing them is how wiring overheats. When in doubt, use the lower number.

Further derating applies for high ambient temperature and for more than three current-carrying conductors in a raceway. Those factors multiply, and in a hot roof space with a full conduit they can take a nominal 25 A down below 15 A.

AWG reference table

Copper, at 20 °C. Free-air and bundled ampacity as described above.

AWG and metric do not line up

Metric cable is specified directly by cross-section in mm², in a standard series — 0.5, 0.75, 1, 1.5, 2.5, 4, 6, 10 and so on. AWG sizes fall between these, so conversions are always approximate:

Note the direction: 14 AWG is meaningfully smaller than 2.5 mm², despite often being listed as equivalent. Substituting one for the other in a design that was close to its limit is not safe. When sourcing internationally, compare the mm² figures rather than trusting an equivalence table.

Stranded versus solid

For the same AWG number, stranded wire has slightly less copper than solid — the strands cannot pack perfectly, so there are air gaps — and a slightly larger overall diameter. The current rating is treated as the same.

The choice is mechanical. Solid holds its shape, sits reliably in screw terminals and push-fit connectors, and is standard for fixed building wiring. Stranded flexes without fatiguing, which matters for anything that moves, gets handled, or is subject to vibration. Stranded wire in a screw terminal should be ferruled rather than tinned — solder cold-flows under pressure and the joint loosens over time.

Choosing a size

1. Start with ampacity for how the wire will actually be installed, not the free-air figure.
2. Apply the 80% rule if the load runs continuously for more than three hours.
3. Derate for temperature and grouping if the wire runs somewhere hot or shares a conduit with several others.
4. Check voltage drop over the actual run length. Past 20–30 m this usually demands a larger size than ampacity alone.
5. Take the larger of the two. Ampacity protects the wire; voltage drop protects the load.

How this calculator is checked

Technical reviewer

Salamot Hok

Electrician · 10+ years of installation work in Bangladesh and the wider South Asian region

He reads the result the way an installer would: are the defaults values people actually meet, does the warning fire where you would stop and think, and is the answer something you could buy and fit? The code figures themselves come from the published standards cited below, not from him — that boundary is set out on his profile.

• The maths lives in a pure function with its own test suite, asserted against worked examples from published references and standards. A calculator does not ship until those tests pass.
• 3 sources cited by name and linked, so any figure on the page can be traced back to the document it came from.
• Last reviewed 12 August 2026. Review dates are advanced only when the page is actually re-read, never to look fresh.
• Unusable input returns no answer. Where the inputs do not describe a real design, the calculator says so and withholds the number rather than printing a plausible-looking wrong one.

The full process is written up in the methodology and editorial policy. Results are engineering guidance, not a code sign-off — see the disclaimer. If a result looks wrong, tell us; corrections are answered before anything else.