About the SWG to mm Calculator
Standard Wire Gauge (SWG), also called the Imperial or British Standard Wire Gauge, is still used in the UK, India and many other countries for enamelled copper wire, jewellery wire, springs and sheet metal. Bigger numbers mean thinner wire. This calculator converts any SWG from 7/0 down to 50 into millimetres and inches, gives the cross-section area in mm², and shows the closest American Wire Gauge (AWG). You can also go the other way and find the SWG nearest to a measured diameter.
Updated October 2026
How to use the SWG to mm Calculator
- 1Choose SWG to mm, or mm to nearest SWG.
- 2Pick the gauge from the list, or type the diameter in millimetres.
- 3Read the diameter, area and nearest AWG.
- 4Open the full chart for every gauge at once.
- 5Copy the result if you need it.
Where SWG is still used
Although metric sizes have replaced it for most electrical cable, SWG lives on in transformer and motor winding wire, guitar strings, jewellery wire, fencing wire, springs and some sheet metal. Many Indian and UK suppliers still list enamelled copper wire by SWG, so a quick conversion avoids buying the wrong size.
Reading the gauge numbers
The scale runs backwards: the larger the number, the thinner the wire. Gauges thicker than 0 are written 2/0, 3/0 and so on up to 7/0. The steps are not equal; the diameter falls quickly at the thick end and slowly at the thin end.
- 10 SWG = 3.251 mm
- 14 SWG = 2.032 mm
- 18 SWG = 1.219 mm
- 24 SWG = 0.559 mm
- 30 SWG = 0.315 mm
- 36 SWG = 0.193 mm
Area and current
Current capacity depends on the cross-section area, not the diameter, and area rises with the square of the diameter. Doubling the diameter gives four times the copper. The calculator shows the area so you can compare wire sizes properly or check winding tables that list mm².
Converting between SWG and AWG
AWG sizes follow a formula, so every step is about 11% thinner than the last, while SWG sizes come from a table set in 1884. They rarely match exactly. When a design calls for one and your supplier sells the other, pick the closest size with an area at least as large as the original if the wire carries current.
On site or at the workbench
Use it on a phone next to the reel or on a computer while you plan a winding. Nothing you enter is sent anywhere. Wire size affects more than width. Use the Wire Gauge Calculator for AWG sizes, the Wire Resistance Calculator for loss, and the Voltage Drop Calculator for long runs.
Features
- Every SWG from 7/0 to 50
- Diameter in mm and inches
- Cross-section area in mm²
- Nearest AWG for comparison
- Reverse lookup from a diameter
- Full printable chart
Frequently asked questions
What is 22 SWG in mm?
22 SWG is 0.028 inches, which is 0.7112 mm, with a cross-section of about 0.397 mm².
Is SWG the same as AWG?
No. Both get thinner as the number rises, but the sizes differ. For example 20 SWG is 0.914 mm while 20 AWG is 0.812 mm. The calculator shows the closest AWG so you can compare.
What is the thickest SWG?
7/0 SWG is 0.5 inches, or 12.7 mm. The thinnest standard gauge, 50 SWG, is 0.001 inches, or 0.0254 mm.
How do I find the SWG of a wire I have?
Measure its diameter with a micrometer or calipers, removing enamel or insulation first, then use mm to nearest SWG.
Does SWG apply to sheet metal?
Sheet metal gauges in the UK often follow SWG, but steel, aluminium and galvanised sheet can use other gauge tables. Check the supplier's table when it matters.
Can I use this to choose cable for mains wiring?
Mains cable is sold by cross-section area in mm², not SWG. This tool helps with winding wire and craft wire; follow your local wiring rules for house cables.