American wire gauge

American Wire Gauge (AWG) 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.

:<math>n = -39\log_{92} \left( \frac{d_n}{0.005~\mathrm{inch \right) + 36 = -39\log_{92} \left( \frac{d_n}{0.127~\mathrm{mm \right) + 36</math>

and the cross-section area is

:<math>A_n = \frac{\pi}{4} d_n^2 \approx 0.000019635~\mathrm{inch}^2 \times 92^{(36 - n)/19.5} \approx 0.012668~\mathrm{mm}^2 \times 92^{(36 - n)/19.5}</math>.

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 . ASTM B258-02 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 thicker than 44 AWG, and 0.00001 inches (0.01 mils) for wires 45 AWG and thinner.

Sizes with multiple zeros are successively thicker than 0 AWG and can be denoted using "number of zeros/0", for example 4/0 AWG for 0000 AWG. For an /0 AWG wire, use in the above formulas. For instance, for 0000 AWG or 4/0 AWG, use .

Rules of thumb

The sixth power of <math>\sqrt[39]{92}</math> is very close to 2, which leads to the following rules of thumb:

When the cross-sectional area of a wire is doubled, the AWG will decrease by 3; for example, two 14 AWG wires have about the same cross-sectional area as a single 11 AWG wire. This doubles the electrical conductance.
When the diameter of a solid round wire is doubled, the AWG will decrease by 6; for example, 1 mm diameter wire is ≈18 AWG, 2 mm diameter wire is ≈12 AWG, and 4 mm diameter wire is ≈6 AWG. This quadruples the cross-sectional area and conductance.
A decrease of ten gauge numbers; for example, from 24 AWG to 14 AWG multiplies the area, weight, and conductance by approximately 10.

Convenient coincidences result in the following rules of thumb for resistances:

The resistance of copper wire is approximately for 10 AWG, for 20 AWG, for 30 AWG, and so on. For an arbitrary gauge n, it is approximately 10n/10 Ω per .
Because aluminum wire has a conductivity of approximately 61% of copper, an aluminum wire has nearly the same resistance as a copper wire that is two sizes smaller, which has 62.9% of the area.

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 wire area. Fusing current (melting wire) is estimated based on 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.

{|class="wikitable sortable mw-collapsible mw-datatable sticky-header-multi" style="text-align:center"

! rowspan=4 | AWG

! rowspan=3 colspan=2 | Diameter

! rowspan=3 colspan=2 | Turns of wire, without insulation

! rowspan=3 colspan=2 | Area

! colspan=8 | Copper wire

! rowspan=2 colspan=2 | Length-specific resistance

! colspan=3 rowspan=2 | Ampacity at temperature rating (A)

! colspan=3 | Fusing current

! Preece

! colspan=2 | Onderdonk

Electrical conductor
Electrical wiring
Number 8 wire, a term used in the New Zealand vernacular

References

External links

Interactive Wire Size and Voltage Drop Calculator (AWG/mm²) — Tool for calculating required wire gauge and voltage drop based on circuit length, current, and temperature compensation.
ASTM B258 Standard Specification for AWG Sizes