AWG to mm² Converter and Wire Gauge Chart (with kcmil)

What does AWG mean?

AWG stands for American Wire Gauge, the North American gauge system for solid round electrical wire. A larger AWG number means a smaller wire.

The gauge is fixed by two diameters: 0.4600 in for 4/0 (0000) and 0.0050 in for 36 AWG. The 38 sizes between them form a geometric progression, so each step changes the diameter by the 39th root of 92, about 1.1229.

Three rules of thumb follow from that ratio. Each gauge step changes the cross-section by about 26 %. Three steps roughly double or halve the area, and six steps roughly double or halve the diameter.

Gauges larger than 1 AWG are 1/0, 2/0, 3/0 and 4/0, also written 0, 00, 000 and 0000 and spoken as “one-aught” to “four-aught”. Above 4/0, conductors are named by their area in kcmil. In catalogs and drawings, “#2” and “No. 2” both mean 2 AWG.

The gauge sizes are specified today in ASTM B258, Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors.

Sources: end points and ratio, NBS Handbook 100 (1966), section 2.2; rules of thumb calculated from that ratio; current standard, ASTM B258-18(2026).

What is kcmil (MCM), and what is a circular mil?

A kcmil is 1,000 circular mils, and a circular mil is the area of a circle 1 mil (0.001 in) across. MCM is the older name for the same unit, so 250 kcmil and 250 MCM are the same size.

Circular mils take π out of the arithmetic. The area of a round wire in circular mils is its diameter in mils, squared. 12 AWG, for example, is 80.81 mil across, so its area is about 6,530 cmil, or 6.530 kcmil.

In SI units, 1 cmil = π/4 × (0.0254 mm)² = 0.000506707479 mm². So 1 kcmil = 0.5067 mm², and 1 mm² is about 1.974 kcmil.

The gauge numbers stop at 4/0, so larger conductors are named directly by area. The chart covers the common kcmil sizes 250, 300, 350, 400, 500, 600, 700, 750, 800, 900, 1000, 1250, 1500, 1750 and 2000 kcmil, starting at the 250 kcmil row.

Sources: circular mil and kcmil, Wikipedia, “Circular mil” and NBS Handbook 100 (1966); kcmil and MCM, Cerrowire, Electrical FAQs, “What is the difference between kcmil and MCM?”; SI constant calculated from 1 mil = 0.0254 mm.

How do you convert AWG to mm² and kcmil?

Find the diameter from the gauge number, then the area: d = 0.005 in × 92^((36 − n)/39), and A = π/4 × d². For 1/0, 2/0, 3/0 and 4/0, n is 0, −1, −2 and −3.

The converter and both charts use these formulas:

d(in)   = 0.005 × 92^((36 − n) / 39)
d(mm)   = 25.4 × d(in)
A(cmil) = (1000 × d(in))²        A(kcmil) = A(cmil) / 1000
A(mm²)  = π/4 × d(mm)² = 0.506707479 × A(kcmil)
n       = 36 − 39 × log₉₂(d(in) / 0.005)

For mm² to AWG, the converter first finds the solid-wire diameter, d = √(4A/π). It then finds the gauge number n with the last line.

The tool and charts calculate at full precision and round only for display, to four significant figures. NBS Handbook 100 records that ASTM B258-61 rounded the formula diameters to the nearest 0.1 mil. The handbook’s other tables are calculated from those rounded diameters, and it prints derived values to four significant figures for 10 AWG and larger.

In area, tables built from rounded diameters can differ from the formula by up to about 0.25 % at 20 AWG and larger. At the finest gauges, the difference reaches about 3 %.

The figure below draws eight common AWG sizes to scale, each inside the next larger IEC metric size.

The four worked examples below show intermediate values rounded to four significant figures. The converter keeps full precision, so recalculating from the rounded values can change the last digit.

Example 1: 12 AWG to mm²

1. Exponent: (36 − 12)/39 = 24/39 = 0.6154.
2. Diameter: d = 0.005 × 92^0.6154 = 0.005 × 16.16 = 0.08081 in, or 2.053 mm.
3. Area in circular mils: 80.81² = 6,530 cmil = 6.530 kcmil.
4. Area in mm²: 6.530 × 0.5067 = 3.309 mm².
5. Result: 12 AWG = 3.309 mm² (6.530 kcmil). The nearest IEC metric size, and also the next larger one, is 4 mm².

Example 2: 2/0 AWG to mm² and kcmil

1. Gauge number: 2/0 means n = −1, so the exponent is (36 + 1)/39 = 37/39 = 0.9487.
2. Diameter: d = 0.005 × 92^0.9487 = 0.005 × 72.96 = 0.3648 in, or 9.266 mm.
3. Area in circular mils: 364.8² ≈ 133,100 cmil = 133.1 kcmil.
4. Area in mm²: π/4 × 9.266² = 67.43 mm².
5. Result: 2/0 AWG = 67.43 mm² (133.1 kcmil). The nearest IEC metric size is 70 mm².

Example 3: 250 kcmil to mm²

1. Area in mm²: 250 × 0.506707479 = 126.7 mm².
2. Area in circular mils: 250 kcmil = 250,000 cmil.
3. Solid wire of that area: √250,000 = 500.0 mil = 0.5000 in, or 12.70 mm.
4. Result: 250 kcmil = 126.7 mm². The nearest IEC metric size is 120 mm², and the next larger is 150 mm².

Example 4: 2.5 mm² to AWG

1. Solid wire of that area: d = √(4 × 2.5/π) = 1.784 mm, or 0.07024 in (70.24 mil).
2. Area in kcmil: 2.5/0.5067 = 4.934 kcmil.
3. Gauge number: n = 36 − 39 × log₉₂(0.07024/0.005) = 36 − 39 × 0.5844 = 13.21, shown as 13.2.
4. Result: the nearest gauge is 13 AWG (2.624 mm²), which is also the smallest gauge that is not smaller. 14 AWG (2.081 mm²) is smaller, and 12 AWG (3.309 mm²) is larger.

Sources: formula, NBS Handbook 100 (1966), section 2.2; 0.1-mil rounding under ASTM B258-61 and rounded derived values, the same handbook, note to table 1; area differences and worked examples calculated.

Why does 2.5 mm² have no exact AWG match?

Because AWG and metric conductors are two separate series. AWG steps by a fixed ratio of diameters, while metric sizes follow a rounded list of cross-sections. A metric size therefore lands between two gauges, and a chart can show only the nearest standard size, not an exact match.

That gives two answers for every metric size: the nearest size by area, and the smallest size that is not smaller. “Nearest” compares sizes by ratio, the way gauge numbers step, so 4/0 AWG (107.2 mm²) is listed nearest to 120 mm² rather than 95 mm². In the mm² to AWG chart, the two differ at 35 mm² (2 AWG and 1 AWG), 70 mm² (2/0 and 3/0), 95 mm² (3/0 and 4/0), 185 mm² (350 and 400 kcmil) and 800 mm² (1500 and 1750 kcmil).

Published charts disagree for the same reason. Some list the closest gauge, some the closest even gauge, and some always round to the smaller gauge.

The metric sizes are the nominal cross-sections of IEC 60228, the international standard for conductors of insulated cables. The standard sets a maximum resistance for each size, not an exact copper area. For the wider picture, see how electrical cables are classified.

Before ordering, ask our engineers to confirm which nominal size the cable will be made and marked in, metric or AWG.

Sources: nearest and not-smaller sizes calculated; IEC 60228:2023.

Does a stranded conductor have the same area as a solid wire?

Not exactly. An AWG size describes a solid round wire. A stranded conductor of the same size is built so that its combined strand area comes close to that figure, and its overall diameter is larger because of the gaps between strands.

Three things move the real copper area away from the chart value: the number and size of the strands, the lay (twisted strands are slightly longer than the cable) and compaction. Compaction closes the gaps and makes the conductor smaller across, not smaller in area; see compact aluminum conductors.

Metric flexible conductors to IEC 60228 are specified by a maximum resistance per size, so their geometric copper area can sit slightly above or below the nominal mm² value. For the choice of construction, see solid, stranded and fine-stranded copper.

When you replace a metric cable with an AWG cable, or the reverse, compare the maximum conductor resistance on both datasheets, not the area figure alone.

Sources: IEC 60228:2023.

Do copper and aluminum wires use the same gauge?

Yes. AWG and kcmil describe geometry, so 1/0 AWG is 53.48 mm² whether the wire is copper or aluminum. What differs is resistance: aluminum conducts less than copper, so an aluminum conductor of the same gauge has a higher resistance.

The same holds for every row of the chart, including 1/0 AWG and 2/0 AWG. For the differences between the two metals, see aluminum vs copper conductors.

Before ordering an aluminum conductor in place of copper, ask our engineers to confirm the conductor the circuit needs.

Sources: AWG definition, NBS Handbook 100 (1966), section 2.2; ASTM B258-18(2026).

What does this converter not cover?

It converts conductor geometry only. It does not give current rating, resistance, voltage drop, insulation thickness or the overall dimensions of a finished cable.

Current rating depends on insulation, installation and the applicable code; for DLO cables, see the DLO cable ampacity chart.

The converter also has these limits:

• Range. It covers 40 AWG to 4/0 AWG, and areas from about 0.005 mm² (40 AWG) to 1,013 mm² (2000 kcmil). Outside that range, it declines and says why.
• Other gauge systems. SWG, BWG and metric gauge numbers are not converted.
• Stranded or compacted conductors. The result is the solid-wire area; see stranded and solid conductors.
• Other units. Values with length or current units, such as “5 ft” or “20 A”, are refused.

Related tools and guides

These pages cover the topics next to this converter:

• All cable tools
• Wire resistance calculator, for the DC resistance of copper and aluminum conductors per km and per 1000 ft
• THHN, THWN-2 and XHHW-2 building wire, the US building-wire types ordered in AWG and kcmil
• 24 AWG and 22 AWG RS-485 data pairs, with the other points to check for a bus cable

Frequently asked questions

Sources: values calculated from the AWG definition in NBS Handbook 100 (1966), section 2.2; ASTM B258-18(2026).

What should you do next?

Use the converter for exact areas, and read both the “nearest” and the “not smaller” columns before you replace one cable with another. Check the conductor resistance and the other electrical values on the datasheet, not the area alone. On the order, state the size in both mm² and AWG. When you are ready, send the size, number of cores, length and standard to our engineers through the contact page.