Convert mm² to AWG.

AWG is a discrete scale, so any arbitrary mm² value won't land on an exact AWG number. The converter returns the closest standard AWG and shows the actual area at that size for comparison.

Formula

d (mm) = 2 × √(A / π)
n (AWG) = 36 − 39 × log₁₀(d / 0.127) / log₁₀(92)

A = cross-sectional area in mm²
d = conductor diameter in mm
n = AWG number (round to nearest standard size)

This is the ASTM B258 formula solved for n. Negative n values mean the aught sizes: n = 0 is 1/0, n = −1 is 2/0, n = −2 is 3/0, n = −3 is 4/0.

Reference values

Values shown are the AWG with the closest cross-sectional area to the IEC standard size. Note that for several sizes (e.g. 2.5 mm² → 13 AWG) the closest match isn't the AWG that's typically informally cross-referenced (you'll often see "2.5 mm² ↔ 14 AWG" but 14 AWG is actually only 2.08 mm²). For ampacity-critical work, pick the AWG whose area is at least as large as the IEC size you would have used.

Things to watch for

• Round in the direction that increases ampacity. When substituting one size for another for a current-carrying application, always pick the size whose actual area is at least as large. For 2.5 mm² → AWG, the answer is "use 12 AWG (3.31 mm²)" not "14 AWG (2.08 mm²)" if you can't tolerate area reduction.
• Standard IEC sizes are spaced wider at the top. IEC steps 50 → 70 → 95 → 120 → 150 → 185 → 240 mm² roughly double every two steps. AWG aught sizes (1/0 → 2/0 → 3/0 → 4/0) step at finer increments, so 4/0 ≈ 107 mm² sits between the 95 and 120 IEC standards.
• Code references. NEC ampacity tables use AWG and kcmil; IEC tables use mm². Don't try to look up one in the other's table — find the local code's ampacity for the size you actually have.
• Cable jackets are sized differently. The mm² rating describes the copper cross-section, not the outer cable diameter. Two cables both rated 2.5 mm² can have very different outer diameters depending on insulation and number of conductors.

What is a square millimeter?

A unit of cross-sectional area equal to one millimeter by one millimeter, used to specify wire conductor size in IEC standards. Electrical wire sizing in most countries outside North America, per IEC 60228.

What is a American Wire Gauge?

AWG is a logarithmic wire-size scale defined by ASTM B258. The diameter formula is d = 0.005 × 92^((36−n)/39) in. Smaller AWG numbers mean thicker wire. Electrical wire sizing in the US, Canada, and parts of Latin America.

How to convert square millimeter to American Wire Gauge

To convert a value from square millimeter (mm²) to American Wire Gauge (AWG), apply the conversion factor shown in the formula above. The calculation is the same whether you do it by hand, in a spreadsheet, or with the live converter on this page.

Steps:

1. Take your input value in mm².
2. Apply the formula d (mm) = 2 × √(A / π) n (AWG) = 36 − 39 × log₁₀(d / 0.127) / log₁₀(92) A = cross-sectional area in mm² d = conductor diameter in mm n = AWG number (round to nearest standard size).
3. The result is your value in AWG.

For repeated calculations, save the formula in a spreadsheet or use the live converter at the top of this page — it handles the math automatically and displays the result as you type.

Frequently asked questions

How do I convert mm² to AWG?

Apply the formula mm² → AWG shown above, or just type your value into the converter at the top of this page. The result updates instantly.

Which is bigger, mm² or AWG?

This depends on the conversion ratio in the formula. If the factor multiplied by your value gives a larger number, then AWG is the smaller unit (so it takes more of them to express the same quantity). If the result is smaller, then AWG is the larger unit.

When would I use mm² versus AWG?

Both units measure electrical, so the choice depends on context. Square millimeter is typically used for wiring specifications and equipment ratings; American Wire Gauge similarly. Most professional fields standardize on one or the other based on regional conventions or technical tradition.

How precise is this mm² to AWG conversion?

The conversion factor shown is the internationally defined exact value (or the best-published approximation if the relationship is irrational, like degrees-to-radians). The live converter on this page uses double-precision floating-point math, accurate to about 15 significant digits — far beyond any practical engineering need.

Is the conversion ratio exact, or an approximation?

Most unit conversions between SI metric units, and between SI and US customary units, have been formally defined as exact values since the 1959 international yard-pound agreement and subsequent SI redefinitions. Exceptions are unit pairs that involve irrational numbers (radians, e.g.) or empirical conversions (like food calories, which depend on temperature). When in doubt, consult the formula at the top of this page.

Related conversions

See also