AWG identifies a conductor size through a geometric gauge series; kcmil states its cross-sectional area in thousands of circular mils. For example, 12 AWG has a nominal solid-wire diameter of approximately 2.053 mm and an area of 3.31 mm², while 250 kcmil converts to approximately 126.68 mm². These are dimensional relationships—not ampacity ratings or approvals to substitute a metric cable.
The charts below distinguish conductor metal area from bare-conductor diameter and finished cable diameter. That distinction matters when comparing wire specifications, checking terminals, or obtaining dimensions for raceway calculations.
AWG Wire Size Chart: Diameter and Cross-Sectional Area
For numbered AWG sizes, a lower number means a larger conductor. Beyond 1 AWG, the sequence continues through 1/0, 2/0, 3/0, and 4/0. These are also written as 0, 00, 000, and 0000. The diameter progression and gauge notation are described in National Bureau of Standards Handbook 100, Copper Wire Tables, Section 2.
The following table contains selected AWG sizes. Values are calculated from the geometric AWG relationship given below and rounded independently. Diameter means the nominal diameter of a solid, round, bare conductor—not the outside diameter of a stranded conductor or insulated wire.
| AWG size | Solid diameter, in | Solid diameter, mm | Metal area, mm² | Metal area, kcmil |
|---|---|---|---|---|
| 36 | 0.00500 | 0.127 | 0.0127 | 0.02500 |
| 34 | 0.00630 | 0.160 | 0.0201 | 0.03975 |
| 32 | 0.00795 | 0.202 | 0.0320 | 0.06321 |
| 30 | 0.01003 | 0.255 | 0.0509 | 0.1005 |
| 28 | 0.01264 | 0.321 | 0.0810 | 0.1598 |
| 26 | 0.01594 | 0.405 | 0.129 | 0.2541 |
| 24 | 0.02010 | 0.511 | 0.205 | 0.4040 |
| 22 | 0.02535 | 0.644 | 0.326 | 0.6424 |
| 20 | 0.03196 | 0.812 | 0.518 | 1.022 |
| 18 | 0.04030 | 1.024 | 0.823 | 1.624 |
| 16 | 0.05082 | 1.291 | 1.31 | 2.583 |
| 14 | 0.06408 | 1.628 | 2.08 | 4.107 |
| 12 | 0.08081 | 2.053 | 3.31 | 6.530 |
| 10 | 0.10190 | 2.588 | 5.26 | 10.38 |
| 8 | 0.12849 | 3.264 | 8.37 | 16.51 |
| 6 | 0.16202 | 4.115 | 13.3 | 26.25 |
| 4 | 0.20431 | 5.189 | 21.2 | 41.74 |
| 3 | 0.22942 | 5.827 | 26.7 | 52.63 |
| 2 | 0.25763 | 6.544 | 33.6 | 66.37 |
| 1 | 0.28930 | 7.348 | 42.4 | 83.69 |
| 1/0 | 0.32486 | 8.251 | 53.5 | 105.5 |
| 2/0 | 0.36480 | 9.266 | 67.4 | 133.1 |
| 3/0 | 0.40964 | 10.405 | 85.0 | 167.8 |
| 4/0 | 0.46000 | 11.684 | 107 | 211.6 |
Calculation basis: the AWG geometric progression in NBS Handbook 100, Section 2.2, with geometric area conversion. These are calculated dimensional reference values, not a reproduction of its standardized rounded-diameter tables. The handbook explains that rounding nominal diameters before calculating area can produce small differences between published tables.
How AWG Numbers Relate to Conductor Size
AWG is not a linear diameter scale. Moving one gauge step toward a larger conductor increases diameter by approximately 12.3% and area by approximately 26.1%. Moving three steps toward a larger conductor approximately doubles its area. For example, 9 AWG has approximately twice the metal area of 12 AWG; the relationship does not mean twice the allowable current.
The zero sizes continue the same progression:
- 1/0 is larger than 1 AWG.
- 2/0 is larger than 1/0.
- 3/0 is larger than 2/0.
- 4/0 is larger than 3/0.
Unlike AWG gauge numbers, kcmil values increase directly with conductor area.
kcmil Wire Size Chart: Area and Equivalent Diameter
One circular mil is the area of a circle with a diameter of 0.001 inch. One kcmil equals 1,000 circular mils. A circular mil is an area unit; it is not a square mil.
The following table shows selected kcmil sizes. The equivalent solid diameter is the diameter of a solid circle having the stated metal area. It is not a stranded-conductor outside diameter.
| Conductor size, kcmil | Converted metal area, mm² | Equivalent solid diameter, in | Equivalent solid diameter, mm |
|---|---|---|---|
| 250 | 126.68 | 0.5000 | 12.70 |
| 300 | 152.01 | 0.5477 | 13.91 |
| 350 | 177.35 | 0.5916 | 15.03 |
| 400 | 202.68 | 0.6325 | 16.06 |
| 450 | 228.02 | 0.6708 | 17.04 |
| 500 | 253.35 | 0.7071 | 17.96 |
| 600 | 304.02 | 0.7746 | 19.67 |
| 700 | 354.70 | 0.8367 | 21.25 |
| 750 | 380.03 | 0.8660 | 22.00 |
| 800 | 405.37 | 0.8944 | 22.72 |
| 900 | 456.04 | 0.9487 | 24.10 |
| 1,000 | 506.71 | 1.0000 | 25.40 |
| 1,250 | 633.38 | 1.1180 | 28.40 |
| 1,500 | 760.06 | 1.2247 | 31.11 |
| 1,750 | 886.74 | 1.3229 | 33.60 |
| 2,000 | 1013.41 | 1.4142 | 35.92 |
Values are calculated from the circular-mil definition in NBS Handbook 100, Section 2.1. The displayed decimal places describe a unit conversion; they do not specify manufacturing tolerances or a cable’s measured dimensions.
AWG, kcmil, and mm² Conversion Formulas
Calculate AWG Diameter and Area
For the AWG range shown in the chart:
[
d_{\text{in}}=0.005\times92^{(36-n)/39}
]
[
d_{\text{mm}}=0.127\times92^{(36-n)/39}
]
where:
- (n) is the AWG index.
- (d_{\text{in}}) is solid-wire diameter in inches.
- (d_{\text{mm}}) is solid-wire diameter in millimeters.
Use (n=0) for 1/0, (n=-1) for 2/0, (n=-2) for 3/0, and (n=-3) for 4/0. The progression is anchored by 36 AWG at 0.0050 inch and 4/0 AWG at 0.4600 inch.
Calculate the corresponding round-wire area as:
[
A_{\text{mm}^2}=\frac{\pi}{4}d_{\text{mm}}^2
]
Or calculate circular-mil area from diameter in inches:
[
A_{\text{cmil}}=(1000d_{\text{in}})^2
]
[
A_{\text{kcmil}}=\frac{A_{\text{cmil}}}{1000}
]
For example, entering (n=12) gives:
[
d_{\text{mm}}
=0.127\times92^{24/39}
\approx2.0525\text{ mm}
]
[
A_{\text{mm}^2}
=\frac{\pi}{4}(2.0525)^2
\approx3.3088\text{ mm}^2
]
Rounded for reference, 12 AWG is approximately 2.053 mm in solid diameter and 3.31 mm² in area. Keep unrounded intermediate values when reproducing the chart.
Convert kcmil to mm²
Because one mil is 0.0254 mm:
[
1\text{ cmil}
=\frac{\pi}{4}(0.0254)^2\text{ mm}^2
]
Therefore:
[
A_{\text{mm}^2}
=0.50670748\times A_{\text{kcmil}}
]
The reverse conversion is:
[
A_{\text{kcmil}}
\approx1.97352524\times A_{\text{mm}^2}
]
These equations convert area units; they do not identify an interchangeable cable product. The conversion follows directly from the circular-mil definition.
For example:
[
250\text{ kcmil}\times0.50670748
\approx126.68\text{ mm}^2
]
To obtain an equivalent solid diameter:
[
d_{\text{mm}}
=\sqrt{\frac{4A_{\text{mm}^2}}{\pi}}
]
For 250 kcmil, this gives 12.70 mm. An actual stranded 250 kcmil conductor can have a substantially different outside diameter because its strand arrangement is part of its construction.
Metal Area Is Not Cable Outside Diameter
Three dimensions serve different purposes:
| Dimension | What it describes | Appropriate use |
|---|---|---|
| Conductor metal area | The metal cross section, excluding spaces between strands | Comparing nominal conductor sizes and establishing an area input |
| Bare-conductor outside diameter | The envelope around the conductor’s strands | Checking conductor construction and obtaining product-specific connection dimensions |
| Finished wire or cable outside diameter | The outside dimension including insulation, jackets, and other layers | Obtaining dimensional inputs for raceway, cable-entry, and routing checks |
NBS Handbook 100 distinguishes total strand area from the outside diameter of a stranded conductor in its explanation and tables for concentric-lay cables. Manufacturer specifications provide the actual construction-dependent dimensions.
For a concrete example, Southwire Specification 48305, Table 1, lists a 4/0 AWG Class H rope-lay bare copper conductor with:
- 259 strands.
- A listed conductor area of 211,600 cmil.
- A nominal diameter over the conductor of 0.590 inch.
The AWG chart’s equivalent solid diameter for 4/0 is 0.460 inch. Both values are meaningful: 0.460 inch represents the nominal solid-wire geometry, while 0.590 inch describes that particular stranded product. The manufacturer identifies its dimensions as nominal and subject to manufacturing tolerances.
Do not enter the solid-wire diameters in this chart as finished cable diameters for conduit or cable-tray checks. Obtain the relevant dimensions from the exact cable data sheet, then apply the calculation method and installation rules required for the project.
Converted mm² Area Is Not an Interchangeable Metric Size
A mathematical conversion and a metric cable designation answer different questions.
For example, 12 AWG converts to approximately 3.31 mm². That does not make it a 4 mm² cable, nor does the conversion establish that a 4 mm² cable can replace it in a particular installation.
Southwire’s American Wire Gauge technical reference, Edition 11, Volume 2, separates converted nominal areas from its “closest” metric-to-AWG size table. It specifically explains that the closest sizes associated with UL standards concern insulation and jacket thickness requirements—not general electrical interchangeability.
For a proposed substitution, resolve the following with the actual product documentation and the project’s governing requirements:
- Conductor material and specified electrical resistance.
- Solid or stranded construction, including the strand class accepted by the terminal.
- Insulation voltage rating, temperature rating, and environmental suitability.
- Applicable ampacity basis and installation conditions.
- Terminal conductor-size range and connection requirements.
- Voltage-drop requirements for the circuit.
- Required product approvals and the locally adopted installation standard.
The area charts provide the dimensional comparison at the start of that review. They do not supply the missing product ratings, installation conditions, or jurisdiction-specific requirements.
Using the Reference for Resistance and Loss Calculations
Conductor area can support a resistance calculation when conductor resistivity and length are also known:
[
R=\rho\frac{L}{A}
]
where (R) is resistance in ohms, (\rho) is resistivity in (\Omega\cdot\text{mm}^2/\text{m}), (L) is conductor length in meters, and (A) is metal area in mm². The resistivity must correspond to the conductor material and temperature. NBS Handbook 100 provides copper resistivity and temperature relationships; area alone does not determine resistance.
For a selected cable, use the manufacturer’s resistance data when available, with its stated temperature and length basis. Do not substitute an equivalent solid diameter for a product-specific resistance value.
The Conductor Resistive Loss and Energy Cost Calculator uses a steady current and user-supplied conductor resistance to estimate resistive energy loss and annual energy cost. Its stated calculation excludes reactance, load variation, harmonics, temperature variation, and utility demand charges; the AWG and kcmil charts do not supply those missing operating inputs.