Wire gauge converter
AWG to millimetres and back, from the two diameters that define the scale — and a clear statement of what a gauge does not tell you, which is how much current it can carry. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
AWG is a geometric series, defined by two numbers
36 gauge is 0.005 inches and 0000 gauge is 0.46 inches, with 39 equal geometric steps between them. Everything else follows:
d = 0.005 × 92(36−n)/39
inches
And the famous 92 is not an arbitrary constant — it is 0.46 ÷ 0.005, the ratio between the two gauges that define the scale. The inch is exactly 25.4 mm, so the millimetre form is exact too and is not a separate measurement.
The numbers run backwards
Bigger gauge means thinner wire, because the number originally counted how many times the wire had been pulled through a drawing die. And above gauge 1 it goes to 0, 00, 000, 0000 rather than to negative numbers — which are gauges −1, −2 and −3 in the formula. Software that clamps those at zero makes 4/0 cable the same size as 1/0, which is a factor of two in area.
The rules of thumb, measured
| Three gauges doubles the area | Really 2.005×. Close enough to use. |
|---|---|
| Six gauges is four times | Really 4.020×. |
| Ten gauges is ten times | Really 10.16× — 1.6% out, and still the most useful one to remember. |
A gauge is a diameter, not an ampacity
This is the important one. Nothing here tells you how much current a cable can carry. That depends on the insulation's temperature rating, how many conductors are bundled together, the ambient temperature, whether the run is in free air or in a conduit or buried, how long it is, and what the regulations where you live actually require. The same 12 AWG wire is rated 20 A in one table and 30 A in another, and both are right for their conditions.
Use the published tables for your jurisdiction — BS 7671 in the UK, the NEC in the United States — and if it is mains wiring, use an electrician.
Metric cable is sized by area, not diameter
European cable is quoted in square millimetres of conductor — 1.5 mm², 2.5 mm², 6 mm² — and those are nominal sizes from a standard series, not exact areas. They rarely land on an AWG value, so the conversion is a nearest-equivalent rather than a translation: 2.5 mm² sits between 14 and 13 AWG. And stranded cable's overall diameter is bigger than a solid conductor of the same area, because of the gaps between the strands.
What it will not do
- It will not give you an ampacity. See above, twice.
- It will not handle stranded construction. The area is the sum of the strands; the diameter is not.
- It will not do SWG, the British Standard Wire Gauge, which is a different and non-geometric series that happens to use similar numbers.