Swg to Awg Converter
Convert between Standard Wire Gauge (British) and American Wire Gauge. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Swg to Awg Converter
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Formula: Compare SWG diameter (lookup table) to AWG diameter = 0.127 x 92^((36-AWG)/39)
Worked example โ SWG 12 (5.48 mm2) is closest to AWG 10 (5.26 mm2) | Use AWG 10 or upsize to AWG 9
Formula
Compare SWG diameter (lookup table) to AWG diameter = 0.127 x 92^((36-AWG)/39)
SWG diameters are defined by a fixed lookup table from British Standard 3737. AWG diameters follow a mathematical formula. Conversion finds the AWG size whose diameter most closely matches the SWG diameter, or vice versa.
Worked Examples
Example 1: Converting Indian SWG Specification to US AWG
Problem:An Indian electrical specification calls for SWG 12 copper wire. What AWG size should be used for a US installation?
Solution:SWG 12 diameter = 2.642 mm SWG 12 area = PI x (2.642/2)^2 = 5.480 mm2 AWG 10 = 5.261 mm2 (slightly smaller) AWG 9 = 6.631 mm2 (slightly larger) For safety, choose AWG 10 (close match) or AWG 9 (extra margin)
Result:SWG 12 (5.48 mm2) is closest to AWG 10 (5.26 mm2) | Use AWG 10 or upsize to AWG 9
Example 2: Guitar String Gauge Conversion
Problem:A British guitar string set lists the high E string as SWG 26 (0.457 mm). What is this in AWG and inches?
Solution:SWG 26 diameter = 0.457 mm In inches: 0.457 / 25.4 = 0.0180 inches (approximately .018) Closest AWG: AWG 25 = 0.455 mm (very close match) AWG 26 = 0.405 mm (too thin) The string is approximately 18 thousandths of an inch
Result:SWG 26 (0.457 mm) = approximately AWG 25 (0.455 mm) = 0.018 inches
Frequently Asked Questions
What is the difference between SWG and AWG wire gauge systems?
SWG (Standard Wire Gauge, also called Imperial Wire Gauge or British Standard Wire Gauge) and AWG (American Wire Gauge) are two different systems for measuring wire diameter. SWG was established in Britain in 1883 and is based on a set of standardized diameter values defined in imperial measurements. AWG was developed in the United States and uses a mathematical formula where each gauge step changes the diameter by a constant ratio. The key practical difference is that for the same gauge number, SWG wire is generally thicker than AWG wire. For example, SWG 14 has a diameter of 2.032 mm while AWG 14 is 1.628 mm. This means the same gauge number in each system carries different current capacities and has different resistance values.
Where is SWG still used today?
SWG remains in use primarily in the United Kingdom, India, parts of the Middle East, and several former British Commonwealth countries. In the UK, SWG is used alongside metric sizing for certain applications, particularly in traditional industries and older installations. India widely uses SWG for electrical wiring in residential and commercial buildings, though metric standards are gradually being adopted. The wire and cable industries in Pakistan, Bangladesh, and some African nations also reference SWG sizes. In music, SWG is commonly used for guitar and instrument strings manufactured in Britain. While the international trend is toward metric (mm2) wire sizing as specified by IEC standards, SWG persists in regions with historical British influence and legacy electrical infrastructure.
Why do SWG and AWG give different sizes for the same gauge number?
SWG and AWG differ because they were developed independently using different methodologies. AWG follows a strict mathematical progression where the ratio between consecutive diameters is constant (the 39th root of 92, approximately 1.123). This means AWG sizes can be calculated precisely using a formula. SWG, however, was established empirically based on common wire sizes in use during the 19th century British industrial era. The SWG diameters were standardized from practical manufacturing sizes rather than derived from a mathematical formula. As a result, the progression between SWG sizes is not perfectly geometric, and the diameters at any given gauge number differ from AWG. Both systems share the counterintuitive convention where larger numbers indicate smaller wire diameters.
How do you find the closest AWG equivalent for a given SWG size?
To find the closest AWG equivalent for an SWG wire, first look up the SWG diameter in millimeters from the SWG reference table. Then compare this diameter to AWG diameters calculated using the formula d = 0.127 times 92 to the power of (36 minus AWG) divided by 39. Find the AWG size with the diameter closest to the SWG value. For example, SWG 18 has a diameter of 1.219 mm. Calculating AWG diameters, AWG 17 is 1.150 mm and AWG 16 is 1.291 mm. Since 1.219 mm is closer to 1.150 mm, AWG 17 is the nearest equivalent. However, for electrical applications, always choose the AWG size with equal or greater cross-sectional area to ensure adequate current carrying capacity.
Can SWG and AWG wires be used interchangeably in electrical projects?
SWG and AWG wires should not be used interchangeably without careful verification because the same gauge number corresponds to different physical dimensions. Using the wrong system could result in undersized wire that overheats or oversized wire that does not fit in connectors and conduits. For example, if a UK specification calls for SWG 14 (2.032 mm diameter, 3.243 mm2 area) and you substitute AWG 14 (1.628 mm diameter, 2.081 mm2 area), you get a wire with 36 percent less cross-sectional area, significantly reducing current capacity. Always verify the actual cross-sectional area in mm2 and ensure the replacement wire meets or exceeds the required ampacity. Converting to a common metric unit (mm2) is the safest approach when mixing components from different gauge systems.
What metric wire sizes correspond to common SWG gauges?
Common SWG gauges map to the following approximate metric equivalents: SWG 10 (3.251 mm diameter) is approximately 8.30 mm2, closest to IEC 10 mm2 standard. SWG 12 (2.642 mm) is approximately 5.48 mm2, closest to IEC 6 mm2. SWG 14 (2.032 mm) is approximately 3.24 mm2, closest to IEC 4 mm2. SWG 16 (1.626 mm) is approximately 2.08 mm2, closest to IEC 2.5 mm2. SWG 18 (1.219 mm) is approximately 1.17 mm2, closest to IEC 1.5 mm2. SWG 20 (0.914 mm) is approximately 0.66 mm2, closest to IEC 0.75 mm2. When substituting metric wire for SWG, always round up to the next standard metric size to ensure adequate current carrying capacity.
How do SWG sizes affect guitar and musical instrument strings?
In the musical instrument industry, SWG is commonly used by British and some European string manufacturers to specify string diameters, while American manufacturers typically use inches or AWG. Guitar string gauges affect tone, playability, and tension. A set of light electric guitar strings might be labeled as SWG 20, 17, 14, 10 for the plain strings, corresponding to diameters of 0.914 mm, 1.422 mm, 2.032 mm, and 3.251 mm. American equivalents would be expressed in thousandths of an inch (0.036, 0.056, 0.080, 0.128). Musicians ordering strings from international suppliers must understand both systems to get the correct gauges. Even small diameter differences affect string tension and can require truss rod adjustments on guitars.
What historical factors led to having two different wire gauge standards?
The existence of two wire gauge standards reflects the independent industrialization of Britain and America in the 19th century. Britain established SWG in 1883 through the British Board of Trade as a standardization of the various wire gauges used by different manufacturers. Before SWG, there were over a dozen competing British wire gauge systems. The American wire industry separately developed AWG (originally called Brown and Sharpe gauge after the company that standardized it in 1857) based on a mathematical progression designed for the wire drawing process. Both countries needed standardized wire sizing for the rapidly expanding telegraph and electrical industries but developed solutions independently. The metric system (mm2) was later adopted internationally as the IEC standard to resolve this confusion, but legacy usage of both SWG and AWG persists.
How do you convert SWG to AWG for purchasing wire from international suppliers?
When purchasing wire internationally, follow these steps for accurate conversion. First, identify the SWG size specified in your design or local code. Second, look up the SWG diameter in millimeters from the British standard table. Third, calculate the cross-sectional area in mm2 using the formula pi times radius squared. Fourth, find the AWG size with the nearest cross-sectional area, always rounding to the next larger size for safety. Fifth, verify that the AWG wire meets all electrical requirements including ampacity, voltage drop, and insulation rating for your application. For bulk orders, specify the wire in mm2 rather than either gauge system, as mm2 is universally understood by wire manufacturers worldwide. Many international distributors list all three specifications (SWG, AWG, and mm2) in their catalogs.
What are the limitations of using gauge numbers instead of metric measurements for wire?
Gauge-based wire sizing has several significant limitations compared to metric measurements. The counterintuitive numbering where bigger numbers mean smaller wire causes frequent confusion and errors. The non-linear relationship between gauge numbers and physical dimensions makes mental estimation difficult. Different gauge systems (SWG, AWG, BWG, MWG) use the same numbers for different sizes, creating dangerous potential for mix-ups. Gauge numbers do not directly indicate cross-sectional area, which is the property that actually determines current capacity. The international standard IEC 60228 uses mm2 cross-sectional area, which directly relates to electrical performance and eliminates ambiguity. Modern engineering practice favors metric specification, and many countries have officially deprecated gauge-based systems. However, gauge numbering remains deeply embedded in industry practice, particularly in North America and parts of the former British Empire.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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