American wire gauge

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American wire gauge (AWG), also known as the Brown & Sharpe wire gauge, is a logarithmic stepped standardized wire gauge system used since 1857, predominantly in North America, for the diameters of round, solid, nonferrous, electrically conducting wire. Dimensions of the wires are given in ASTM standard B 258. [1] The cross-sectional area of each gauge is an important factor for determining its current-carrying ampacity.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the most populous city is New York City. Most of the country is located contiguously in North America between Canada and Mexico.

Brown & Sharpe is a division of Hexagon AB, a Swedish multinational corporation focused mainly on metrological tools and technology. During the 19th and 20th centuries, Brown & Sharpe was one of the best-known and most influential machine tool builders and was a leading manufacturer of instruments for machinists. Its reputation and influence were such that its name is often considered to be inseparably paired with certain industrial standards that it helped establish, including:

Logarithm Inverse function of exponentiation that also maps products to sums

In mathematics, the logarithm is the inverse function to exponentiation. That means the logarithm of a given number x is the exponent to which another fixed number, the base b, must be raised, to produce that number x. In the simplest case, the logarithm counts the number of occurrences of the same factor in repeated multiplication; e.g., since 1000 = 10 × 10 × 10 = 103, the "logarithm to base 10" of 1000 is 3. The logarithm of x to baseb is denoted as logb (x), or without parentheses, logbx, or even without the explicit base, log x—if no confusion is possible.


Increasing gauge numbers denote decreasing wire diameters, which is similar to many other non-metric gauging systems such as British Standard Wire Gauge (SWG), but unlike IEC 60228, the metric wire-size standard used in most parts of the world. This gauge system originated in the number of drawing operations used to produce a given gauge of wire. Very fine wire (for example, 30 gauge) required more passes through the drawing dies than 0 gauge wire did. Manufacturers of wire formerly had proprietary wire gauge systems; the development of standardized wire gauges rationalized selection of wire for a particular purpose.

IEC 60228

IEC 60228 is the International Electrotechnical Commission's international standard on conductors of insulated cables. The current version is Third Edition 2004-11 Among other things, it defines a set of standard wire cross-sectional areas:

Metric system Decimal system of units of measurement

The metric system is an internationally recognised decimalised system of measurement. It is in widespread use, and where it is adopted, it is the only or most common system of weights and measures. It is now known as the International System of Units (SI). It is used to measure everyday things such as the mass of a sack of flour, the height of a person, the speed of a car, and the volume of fuel in its tank. It is also used in science, industry and trade.

Wire drawing metalworking process

Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die(s). There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels, and stringed musical instruments. Although similar in process, drawing is different from extrusion, because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed at room temperature, thus classified as a cold working process, but it may be performed at elevated temperatures for large wires to reduce forces. It is a best drawing.

The AWG tables are for a single, solid, round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.

AWG is also commonly used to specify body piercing jewelry sizes (especially smaller sizes), even when the material is not metallic. [2]

Body jewelry sizes express the thickness of an item of body jewelry, using one of several possible systems.


By definition, No. 36 AWG is 0.005 inches in diameter, and No. 0000 is 0.46 inches in diameter. The ratio of these diameters is 1:92, and there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Because each successive gauge number increases cross sectional area by a constant multiple, diameters vary geometrically. Any two successive gauges (e.g., A & B ) have diameters in the ratio (dia. B ÷ dia. A) of (approximately 1.12293), while for gauges two steps apart (e.g., A, B, & C), the ratio of the C to A is about 1.122932 = 1.26098. The diameter of a No. n AWG wire is determined, for gauges smaller than 00 (36 to 0), according to the following formula:

(see below for gauges larger than No. 0 (i.e., No. 00, No. 000, No. 0000 ).)

or equivalently:

The gauge can be calculated from the diameter using  [3]

and the cross-section area is


The standard ASTM B258 - 02(2008) Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors defines the ratio between successive sizes to be the 39th root of 92, or approximately 1.1229322. [4] ASTM B 258-02 also dictates that wire diameters should be tabulated with no more than 4 significant figures, with a resolution of no more than 0.0001 inches (0.1 mils) for wires larger than No. 44 AWG, and 0.00001 inches (0.01 mils) for wires No. 45 AWG and smaller.

Sizes with multiple zeros are successively larger than No. 0 and can be denoted using "number of zeros/0", for example 4/0 for 0000. For an m/0 AWG wire, use n = −(m − 1) = 1 − m in the above formulas. For instance, for No. 0000 or 4/0, use n = −3.

Rules of thumb

The sixth power of 3992 is very close to 2, [5] which leads to the following rules of thumb:

Approximate resistance of copper wire [6] :27

Tables of AWG wire sizes

The table below shows various data including both the resistance of the various wire gauges and the allowable current (ampacity) based on a copper conductor with plastic insulation. The diameter information in the table applies to solid wires. Stranded wires are calculated by calculating the equivalent cross sectional copper area. Fusing current (melting wire) is estimated based on 25 °C (77 °F) ambient temperature. The table below assumes DC, or AC frequencies equal to or less than 60 Hz, and does not take skin effect into account. "Turns of wire per unit length" is the reciprocal of the conductor diameter; it is therefore an upper limit for wire wound in the form of a helix (see solenoid), based on uninsulated wire.

AWGDiameterTurns of wire, without insulationArea Copper wire
Resistance/length [7] Ampacity, [8] at 20 °C insulation material temperature rating,
or for single unbundled wires in equipment for 16 AWG and smaller [9]
Fusing current [10] [11]
60 °C75 °C90 °CPreece [12] [13] [14] [15] Onderdonk [16] [15]
(in)(mm)(per in)(per cm)(kcmil)(mm2)(mΩ/m [lower-alpha 1] )(mΩ/ft [lower-alpha 2] )(A)~10 s1 s32 ms
0000 (4/0)0.4600 [lower-alpha 3] 11.684 [lower-alpha 3] 2.170.8562121070.16080.049011952302603.2 kA33 kA182 kA
000 (3/0)0.409610.4052.440.96116885.00.20280.061801652002252.7 kA26 kA144 kA
00 (2/0)0.36489.2662.741.0813367.40.25570.077931451751952.3 kA21 kA115 kA
0 (1/0)0.32498.2513.081.2110653.50.32240.098271251501701.9 kA16 kA91 kA
10.28937.3483.461.3683.742.40.40660.12391101301451.6 kA13 kA72 kA
20.25766.5443.881.5366.433.60.51270.1563951151301.3 kA10.2 kA57 kA
30.22945.8274.361.7252.626.70.64650.1970851001151.1 kA8.1 kA45 kA
40.20435.1894.891.9341.721.20.81520.2485708595946 A6.4 kA36 kA
50.18194.6215.502.1633.116.81.0280.3133795 A5.1 kA28 kA
60.16204.1156.172.4326.313.31.2960.3951556575668 A4.0 kA23 kA
70.14433.6656.932.7320.810.51.6340.4982561 A3.2 kA18 kA
80.12853.2647.783.0616.58.372.0610.6282405055472 A2.5 kA14 kA
90.11442.9068.743.4413.16.632.5990.7921396 A2.0 kA11 kA
100.10192.5889.813.8610.45.263.2770.9989303540333 A1.6 kA8.9 kA
110.09072.30511.04.348.234.174.1321.260280 A1.3 kA7.1 kA
120.08082.05312.44.876.533.315.2111.588202530235 A1.0 kA5.6 kA
130.07201.82813.95.475.182.626.5712.003198 A798 A4.5 kA
140.06411.62815. A633 A3.5 kA
150.05711.45017.56.903.261.6510.453.184140 A502 A2.8 kA
160.05081.29119.77.752.581.3113.174.01618117 A398 A2.2 kA
170.04531.15022.18.702.051.0416.615.06499 A316 A1.8 kA
180.04031.02424.89.771.620.82320.956.38510141683 A250 A1.4 kA
190.03590.91227.911.01.290.65326.428.05170 A198 A1.1 kA
200.03200.81231.312.31.020.51833.3110.1551158.5 A158 A882 A
210.02850.72335.113.80.8100.41042.0012.8049 A125 A700 A
220.02530.64439.515.50.6420.32652.9616.143741 A99 A551 A
230.02260.57344.317.40.5090.25866.7920.3635 A79 A440 A
240.02010.51149.719.60.4040.20584.2225.672.13.529 A62 A348 A
250.01790.45555.922.00.3200.162106.232.3724 A49 A276 A
260.01590.40562.724.70.2540.129133.940.811.32.220 A39 A218 A
270.01420.36170.427.70.2020.102168.951.4717 A31 A174 A
280.01260.32179.131.10.1600.0810212.964.900.831.414 A24 A137 A
290.01130.28688.835.00.1270.0642268.581.8412 A20 A110 A
300.01000.25599.739.30.1010.0509338.6103.20.520.8610 A15 A86 A
310.008930.22711244.10.07970.0404426.9130.19 A12 A69 A
320.007950.20212649.50.06320.0320538.3164.10.320.537 A10 A54 A
330.007080.18014155.60.05010.0254678.8206.96 A7.7 A43 A
340.006300.16015962.40.03980.0201856.0260.90.180.35 A6.1 A34 A
350.005610.14317870.10.03150.01601079329.04 A4.8 A27 A
360.00500 [lower-alpha 3] 0.127 [lower-alpha 3] 20078.70.02500.01271361414.84 A3.9 A22 A
370.004450.11322588.40.01980.01001716523.13 A3.1 A17 A
380.003970.10125299.30.01570.007972164659.63 A2.4 A14 A
390.003530.08972831110.01250.006322729831.82 A1.9 A11 A
400.003140.07993181250.009890.00501344110491 A1.5 A8.5 A
  1. or, equivalently, Ω/km
  2. or, equivalently, Ω/kft
  3. 1 2 3 4 Exactly, by definition

In the North American electrical industry, conductors larger than 4/0 AWG are generally identified by the area in thousands of circular mils (kcmil), where 1 kcmil = 0.5067 mm2. The next wire size larger than 4/0 has a cross section of 250 kcmil. A circular mil is the area of a wire one mil in diameter. One million circular mils is the area of a circle with 1000 mil (1 inch) diameter. An older abbreviation for one thousand circular mils is MCM.

Stranded wire AWG sizes

AWG gauges are also used to describe stranded wire. The AWG gauge of a stranded wire represents the sum of the cross-sectional areas of the individual strands; the gaps between strands are not counted. When made with circular strands, these gaps occupy about 25% of the wire area, thus requiring the overall bundle diameter to be about 13% larger than a solid wire of equal gauge.

Stranded wires are specified with three numbers, the overall AWG size, the number of strands, and the AWG size of a strand. The number of strands and the AWG of a strand are separated by a slash. For example, a 22 AWG 7/30 stranded wire is a 22 AWG wire made from seven strands of 30 AWG wire.

As indicated in the Formulas and Rules of Thumb sections above, differences in AWG translate directly into ratios of diameter or area. This property can be employed to easily find the AWG of a stranded bundle by measuring the diameter and count of its strands. (This only applies to bundles with circular strands of identical size.) To find the AWG of 7-strand wire with equal strands, subtract 8.4 from the AWG of a strand. Similarly, for 19-strand subtract 12.7, and for 37 subtract 15.6. See the Mathcad worksheet illustration of this straightforward application of the formula.

Calculation of diameter and area in Mathcad AWG calculation in Mathcad software.png
Calculation of diameter and area in Mathcad

Measuring strand diameter is often easier and more accurate than attempting to measure bundle diameter and packing ratio. Such measurement can be done with a wire gauge go-no-go tool such as a Starrett 281 or Mitutoyo 950-202, or with a caliper or micrometer.

Nomenclature and abbreviations in electrical distribution

Alternative ways are commonly used in the electrical industry to specify wire sizes as AWG.

The industry also bundles common wire for use in mains electricity distribution in homes and businesses, identifying a bundle's wire size followed by the number of wires in the bundle.

14/3 and 12/3 cables are also available, used mainly between three-way (two-location) switches, and to have separate wall controls for ceiling fans and their attached light fixtures, or to have one half of a duplex outlet switched and the other always on.

12/2 and 14/2 can also be used for the rare 240-volt-only 15- or 20-amp plug by clearly marking the white wire red or black, since there is no neutral wire. Two conductor cable is available with black and red conductors only for this purpose; the outer sheath is likewise red.

277/480-volt cable is identical to 120/240, except that neutral is grey and hot is yellow (plus an optional orange, used as the red is). The higher voltage, used only in large non-residential buildings, allows more than twice as much electrical power (in watts) to be drawn through the same gauge of wire.

UF-B cable is “underground feeder” cable, which regardless of wire gauge has a solid waterproof grey sheath completely surrounding and filling the space between the conductors, which still have their individual colors. Other types of armored or metallic cable (types AC and MC) have an aluminum casing that may be used as a ground conductor, for which it is not necessary to calculate an equivalent wire gauge.

All new cables are marked as being “with ground” or “w/gnd”, since installation of ungrounded cables has been prohibited by electrical codes for decades. The ground wire is typically the same gauge as the others, despite not being intended to carry large amounts of current for more than a few seconds in the event of a short circuit.


AWG is colloquially referred to as gauge and the zeros in large wire sizes are referred to as aught /ˈɔːt/ . Wire sized 1 AWG is referred to as "one gauge" or "No. 1" wire; similarly, smaller diameters are pronounced "x gauge" or "No. X" wire, where x is the positive integer AWG number. Consecutive AWG wire sizes larger than No. 1 wire are designated by the number of zeros:

and so on.

See also

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  1. "ASTM B258 - 14 Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors". West Conshohocken: ASTM International. Archived from the original on 22 July 2014. Retrieved 22 March 2015.(subscription required)
  2. Body Piercing Jewelry Size Reference — illustrating the different ways that size is measured on different kinds of jewelry
  3. The logarithm to the base 92 can be computed using any other logarithm, such as common or natural logarithm, using log92x = (log x)/(log 92).
  4. ASTM Standard B 258-02, page 4
  5. The result is roughly 2.0050, or one-quarter of one percent higher than 2
  6. Copper Wire Tables (Technical report). Circular of the Bureau of Standards No.31 (3d ed.). United States Department of Commerce. October 1, 1914.
  7. Figure for solid copper wire at 68  °F, (Not in accordance to NEC Codebook 2014 Ch. 9, Table 8) computed based on 100% IACS conductivity of 58.0 MS/m, which agrees with multiple sources: High-purity oxygen-free copper can achieve up to 101.5% IACS conductivity; e.g., the Kanthal conductive alloys data sheet lists slightly lower resistances than this table.
  8. NFPA 70 National Electrical Code 2014 Edition Archived 2008-10-15 at the Wayback Machine . Table 310.15(B)(16) (formerly Table 310.16) page 70-161, "Allowable ampacities of insulated conductors rated 0 through 2000 volts, 60°C through 90°C, not more than three current-carrying conductors in raceway, cable, or earth (directly buried) based on ambient temperature of 30°C." Extracts from NFPA 70 do not represent the full position of NFPA and the original complete Code must be consulted. In particular, the maximum permissible overcurrent protection devices may set a lower limit.
  9. Reference Data for Engineers: Radio, Electronics, Computer and Communications 7th Ed Table 11 "Recommended Current Ratings (Continuous Duty) for electronic equipment and chassis wiring" page 49-16
  10. Computed using equations from H. Wayne Beaty; Donald G. Fink, eds. (2007), The Standard Handbook for Electrical Engineers (15th ed.), McGraw Hill, pp. 4–25, ISBN   978-0-07-144146-9
  11. Douglas Brooks (December 1998), "Fusing Current: When Traces Melt Without a Trace" (PDF), Printed Circuit Design, 15 (12): 53
  12. W. H. Preece (1883), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society (36): 464–471
  13. W. H. Preece (1887), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society, II (43): 280–295
  14. W. H. Preece (1888), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society, III (44): 109–111
  15. 1 2 Douglas G, Brooks; Johannes Adam (29 June 2015), "Who Were Preece and Onderdonk?", Printed Circuit Design and Fab
  16. E. R. Stauffacher (June 1928), "Short-time Current Carrying Capacity of Copper Wire" (PDF), General Electric Review, 31 (6)

Further reading