14 AWG and 2.5 mm² share a row on every chart and differ by a fifth of the copper. And the gauge number itself gets bigger as the wire gets thinner.
Calculator
I have a:
The IACS reference standard — 100% conductivity is defined as this value.
Cross-section2.0809 mm²
Diameter1.6277 mm · 0.06408 in
Resistance8.2848 Ω/km · 2.5252 Ω per 1000 ft
4106.7 circular mils, or 4.107 kcmil, in copper (annealed) at 20 °C.
Against the metric sizes
Nearest stocked metric size
2.5 mm² · +20.1%
Nearest AWG size
14 · 0%
These are not equivalents. The nearest stocked metric size has 20.1% more copper than this conductor. Equivalence charts put them on the same row because the genuinely closest AWG size is often one nobody stocks — treat a substitution as a change to the circuit, not a relabelling.
Voltage drop over a run
Drop7.456 V — 6.21%
Over the 3% commonly recommended for a branch circuit. A thicker conductor, a shorter run or a higher supply voltage each fix it. The run is counted twice because the current has to come back.
Why there is no current rating here
A wire gauge does not have a current rating, and any single number you are given is a code-table entry for a specific installation rather than a property of the copper.
The insulation’s temperature rating — the same conductor in 60 °C, 75 °C and 90 °C insulation carries three different currents, and the terminations may be rated lower than the cable.
Ambient temperature, which derates the figure as it rises and is why a cable in a roof space is not the same as one in a wall.
How many current-carrying conductors are bundled together, since each one heats the others.
The installation method — free air, conduit, buried, in insulation — which changes how the heat leaves.
Which code applies. The US NEC and IEC 60364 tabulate different figures for equivalent conductors, so there is no single correct answer even for one installation.
Whether the limit is heating at all: over a long run the binding constraint is usually voltage drop, which is computed above and often demands a larger conductor than any thermal table would.
Voltage drop, above, is different — it follows from the conductor’s own resistance and nothing else, which is why it can be computed honestly.
What this converter covers
AWG, SWG and mm² with diameter, area, circular mils, resistance per length and voltage drop over a run — every size derived from the AWG formula rather than copied from a table.
AWG 4/0 to 36, SWG, and metric mm² in any direction
Diameter, cross-section, circular mils and kcmil
Resistance per km and per 1000 ft, in copper, aluminium or silver
Voltage drop over a run, with the return path counted
How far the nearest metric size really is — usually 14 to 21%
Derived, not tabulated Metric gap shown Voltage drop Three conductor metals
Planning support from the values you enter — not professional advice.
AWG is a formula, and it runs backwards
American Wire Gauge looks like an arbitrary list of numbers and is not. It is a geometric series pinned at two ends: 36 AWG is exactly 0.005 inches across, 0000 is exactly 0.46 inches, and there are 39 steps between them. Every size in between follows from
d(n) = 0.005 × 92^((36 − n) / 39) inches.
Two useful facts drop straight out of that. Because 92^(6/39) is 2.005, six gauges doubles the diameter and three gauges doubles the area, both to within a quarter of a percent. So 11 AWG has twice the copper of 14 AWG, and 8 AWG has four times. It is worth knowing because it lets you do the arithmetic in your head, and because it explains the shape of the scale.
The two things that trip people up are also consequences of the formula. The numbering runs backwards — a bigger number is a thinner wire, because the gauge originally counted how many times the wire had been drawn through a die, and each pass made it thinner. And the scale is not linear: going up two sizes always means about 59% more copper, but in absolute terms that is 7.85 mm² between 6 and 4 AWG and 0.19 mm² between 22 and 20. The same two-gauge move is forty times more copper at the thick end.
14 AWG is not 2.5 mm²
Every equivalence chart puts 14 AWG and 2.5 mm² on the same line. They are 20% apart. 14 AWG is 2.081 mm²; the metric size has a fifth more copper in it.
Common AWG sizes against the metric size they are usually listed with
AWG
Actual area
Listed as
Metric size is
16
1.309 mm²
1.5 mm²
15% larger
14
2.081 mm²
2.5 mm²
20% larger
12
3.309 mm²
4 mm²
21% larger
10
5.261 mm²
6 mm²
14% larger
The reason the charts do this is worth understanding, because it is not carelessness. The AWG size genuinely closest to 2.5 mm² is 13, which is within 5% — but 13 AWG is an odd size that almost nobody stocks, so the chart rounds to the nearest size you can actually buy and the difference disappears into the row.
Which is fine as long as everyone knows. It stops being fine when a design specified in one system is built in the other and the substitution is treated as a relabelling. A fifth less copper is a fifth more resistance, a fifth more voltage drop and a fifth more heating for the same current — and it goes the other way too, since substituting the metric size where AWG was specified means a conductor that may not fit the terminal it was designed for.
Why there is no current rating on this page
The most-searched question about wire gauge is how many amps a size will carry, and this page will not answer it. That is deliberate, and the reason is not caution for its own sake: a conductor does not have a current rating. Any single number you are given is an entry from a code table for a particular installation, and quoting it without the installation is how the number becomes wrong.
What it actually depends on: the insulation’s temperature rating, so that the same copper in 60 °C, 75 °C and 90 °C insulation carries three different currents — and the terminations at each end may be rated lower than the cable, in which case they set the limit. The ambient temperature, which derates the figure as it rises, so the same cable in a hot roof space is not the same cable as in a cool wall. How many current-carrying conductors are bundled together, since each one heats its neighbours. The installation method — free air, conduit, buried, surrounded by thermal insulation — which decides how the heat gets out. And which code applies: the US NEC and IEC 60364 tabulate different figures for equivalent conductors, so there is not even one right answer for a single installation.
There is also a fifth consideration that quietly overrides the others. On a long run the binding constraint is usually not heating at all but voltage drop, which often demands a larger conductor than any thermal table would. That one is a property of the wire, so it is computed above.
For an actual installation, the figure to use comes from the code that applies where you are, with the correction factors for your conditions, and in most places the work is a licensed electrician’s job. A converter is the wrong place to get it.
Voltage drop, which is a property of the wire
Resistance follows from resistivity, length and cross-section, and nothing else — so unlike ampacity, voltage drop can be computed honestly from the conductor alone.
The detail that gets forgotten is the factor of two. Current has to come back, so a “30 metre run” is 60 metres of conductor and the drop is double what the run length alone suggests. Fifteen amps down 30 metres of 14 AWG copper on a 120 V supply loses 7.46 V — 6.2%, twice the 3% that is commonly recommended for a branch circuit.
Four things move that number, and they are worth knowing in order of leverage. Going up two gauges cuts the drop by 37%, because the resistance falls with the area. Halving the run halves it. Doubling the supply voltage quarters the percentage — the drop in volts halves for the same power, and it is then measured against twice the voltage, which is most of why 230 V countries can run thinner cable over longer distances than 120 V ones. Switching from copper to aluminium makes it 64% worse for the same size, which is why an aluminium conductor generally needs about two gauges more to match.
SWG, and why it disagrees with AWG
Imperial Standard Wire Gauge is the older British system, and it is a genuinely different thing: where AWG is a formula, SWG was defined in 1884 as a table of sizes with no single expression behind it. The steps are irregular by design.
So the two systems share their numbering and agree almost nowhere. SWG 14 is 2.032 mm across; AWG 14 is 1.628 mm — a 25% difference in diameter and 56% in area, from the same number. Even at the top of the scale they differ: SWG 0000 is 0.4 inches against AWG’s 0.46.
SWG is mostly obsolete for electrical cable, where Britain and the Commonwealth moved to metric cross-sections decades ago. It survives in sheet metal, in music-wire and spring-steel sizing, in older tooling, and in knitting and craft supplies — which is exactly where an unlabelled “14 gauge” from an old pattern or an old drawing is most likely to be SWG rather than AWG. If a number comes from a British source before about 1970, that is the way to read it.
Related calculators
Other conversions built on a defining constant:
LengthMillimetres to miles on the exact 1959 factors, with the mil kept clearly apart from the millimetre — they differ 25-fold.
AreaSquare feet, square metres, acres and hectares, with the factors squared for you — a square metre is 10.76 sq ft, not 3.28.
Frequency to WavelengthFrequency, wavelength, photon energy and wavenumber — in vacuum and in the medium, including coax velocity factors.
PowerWatts, kilowatts, horsepower and BTU per hour — with mechanical and metric horsepower listed apart, since they differ by 1.4% under one word.
EnergyJoules, kilojoules, calories, food Calories, kWh, BTU and therms — with the two calories listed apart, since one is a thousand of the other.
Scientific NotationScientific, engineering and decimal forms with significant figures counted — and ambiguous inputs flagged rather than silently resolved.
Every size on this page is computed from the AWG definition rather than read off a table, which is why the figures agree with the published tables to the last digit and why sizes between the tabulated ones are available at all. The sources settle the three things that are conventions rather than arithmetic: the AWG endpoints, the standard metric cross-sections, and the copper resistivity that all the resistance figures come from. The fourth is cited for what this page deliberately does not do.
IEC 60228 — Conductors of insulated cablesInternational Electrotechnical Commission · verified 2026-09-07 · The standard metric conductor cross-sections (0.5, 0.75, 1, 1.5, 2.5, 4, 6 mm² and up) that AWG sizes are compared against here
IEC 60028 — International standard of resistance for copperInternational Electrotechnical Commission · verified 2026-09-07 · The IACS reference: annealed copper at 1.7241 × 10⁻⁸ Ω·m at 20 °C, defined as 100% conductivity, which every resistance figure here is computed from
This page converts sizes and computes resistance. It is not an electrical design tool and it deliberately gives no current rating — see the section above for why a wire does not have one. Electrical work is governed by codes that carry legal force, and in most places some or all of it must be done or certified by a licensed electrician; nothing here replaces the applicable code, the cable manufacturer's own data, or a qualified person's judgement. Three further limits. The resistance figures are for solid conductors at 20 °C: stranded cable has slightly more resistance for a nominal size because of the lay of the strands, and copper's resistance rises about 0.4% per degree, so a hot conductor in a roof space is measurably worse than the table says. The voltage-drop calculation is a DC or resistive one and ignores reactance, which matters on long AC runs and on larger conductors. And an AWG number describes a bare conductor, not a cable: the insulation, the number of cores and the overall diameter are separate specifications that determine what will actually fit through a gland or a conduit.
Published the Wire Gauge Converter: AWG, SWG and metric mm2 with diameter, cross-section, circular mils, kcmil, resistance per length and voltage drop.
Derives every AWG size from the defining formula rather than transcribing a table, which is why the figures agree with the published values to the last digit and why sizes between the tabulated ones are available.
Reports the metric mismatch as a number every time. 14 AWG is 2.081 mm2 against the 2.5 mm2 it is listed with -- 20 percent more copper in the metric size, and 15 to 21 percent across the common sizes. The nearest AWG to 2.5 mm2 is 13, a size nobody stocks, which is why the charts round to 14 and the difference disappears.
Gives NO current rating, deliberately, and explains why: ampacity depends on insulation temperature rating, ambient temperature, bundling, installation method and which code applies, so any single number is a code-table entry for one installation rather than a property of the conductor. The engine exports no ampacity function and the test suite asserts that absence, so a later addition would fail the gate.
Computes voltage drop instead, which does follow from the conductors own resistance, with the return path counted -- a 30 metre run is 60 metres of conductor. Fifteen amps down 30 metres of 14 AWG at 120 V loses 6.2 percent, twice the commonly recommended 3.
Covers SWG as a genuinely different system: defined as an irregular table rather than a formula, so SWG 14 is 56 percent larger in area than AWG 14 despite the shared number.
Verified by 79 automated cases including the exact defining endpoints, the published area table, and a monotonicity sweep across the whole range.
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