Q: What AWG is 2.5 mm²?

2.5 mm² is closest to 14 AWG (2.08 mm²). The metric 2.5 mm² conductor is approximately 20% larger in cross-sectional area than 14 AWG.

Q: What is the diameter of 12 AWG wire?

A 12 AWG solid bare conductor has a diameter of 0.0808 inches (2.05 mm). With THHN insulation, the overall diameter increases to approximately 0.105 inches (2.67 mm).

Q: How do I convert AWG to mm?

Use the formula: diameter (mm) = 0.127 × 92^((36 − AWG) / 39). For cross-sectional area in mm², calculate the diameter first and then use: mm² = π × (diameter/2)².

Q: What is the difference between AWG and kcmil?

AWG is a gauge-based system for conductors up to 4/0. For larger conductors, the industry uses kcmil (thousands of circular mils) which directly describes cross-sectional area. The transition point is 4/0 AWG (211,600 circular mils), with the next standard size being 250 kcmil.

Q: Is 4 mm² the same as 12 AWG?

They are close but not identical. 12 AWG equals 3.31 mm² while 4 mm² is approximately 11 AWG equivalent. A 4 mm² conductor is about 21% larger than 12 AWG and can typically substitute for it since it provides more copper area.

Q: What size wire is 1000 MCM?

1000 MCM (1000 kcmil) has a bare conductor diameter of 1.000 inch (25.4 mm) and a cross-sectional area of 506.7 mm². It is rated for approximately 545 amps at 75°C per NEC Table 310.16.

⚠ Important Notice — For Reference Only

This AWG/metric wire size converter is provided for educational and reference purposes only. Values shown are nominal and based on standard formulas and NEC Chapter 9 data. Actual conductor dimensions may vary by manufacturer, insulation type, and stranding. Always verify wire specifications against the manufacturer’s data sheet before specifying or purchasing cable. Ramcorp Wire & Cable assumes no liability for errors, omissions, or any damages arising from the use of this tool.

AWG to mm & mm to AWG Wire Size Converter

Use this free wire size converter to translate between American Wire Gauge (AWG) and metric (mm²) conductor sizes instantly. Enter an AWG gauge to get the cross-sectional area in mm² and diameter in mm, or enter a metric mm² size to find the nearest AWG equivalent. The complete reference table below covers every standard wire size from 30 AWG through 1000 kcmil with diameter in both inches and millimeters, cross-sectional area in mm² and circular mils, and resistance per 1,000 feet.

Wire Size Converter

AWG ↔ Metric (mm²) — Diameter, area, and resistance for 30 AWG through 1000 kcmil

Select AWG / kcmil Size

Enter Cross-Sectional Area (mm²)

Common metric sizes: 0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500 mm²

Complete AWG to mm Wire Size Reference Table

The table below lists every standard AWG and kcmil conductor size from 30 AWG through 1000 kcmil. All values are for bare solid conductor. Diameters are nominal and based on the standard AWG formula. Cross-sectional areas are shown in both mm² (metric) and circular mils (American). Resistance values are DC resistance for uncoated copper and aluminum conductors at 75°C per NEC Chapter 9, Table 8 (these values are higher than 20°C reference values commonly found in engineering handbooks).

How the AWG System Works

American Wire Gauge is a standardized system for specifying conductor diameter. It follows an inverse logarithmic scale — as the AWG number gets smaller, the wire gets larger. Each step of 3 AWG sizes approximately doubles the cross-sectional area (for example, 10 AWG is about twice the area of 13 AWG), and each step of 6 AWG sizes quadruples it. The gauge number originally corresponded to the number of times the wire was drawn through progressively smaller dies during manufacturing.

The AWG system covers sizes from 0000 (4/0) down to very fine gauges like 40 AWG. For conductors larger than 4/0 AWG, the industry switches to kcmil (thousands of circular mils), sometimes written as MCM. A circular mil is the area of a circle with a diameter of one mil (0.001 inch). For example, a 250 kcmil conductor has a cross-sectional area of 250,000 circular mils.

AWG to Metric Quick Reference

Metric wire sizes used outside the United States are specified by cross-sectional area in mm² rather than by gauge number. The two systems do not align exactly, so conversions are always approximate. The most common equivalences used in international projects are: 14 AWG ≈ 2.5 mm², 12 AWG ≈ 4 mm², 10 AWG ≈ 6 mm², 8 AWG ≈ 10 mm², 6 AWG ≈ 16 mm², 4 AWG ≈ 25 mm², 2 AWG ≈ 35 mm², 1/0 AWG ≈ 50 mm², 2/0 AWG ≈ 70 mm², 3/0 AWG ≈ 95 mm², and 4/0 AWG ≈ 120 mm². These are approximate equivalences — the metric size is typically slightly larger or smaller than the AWG size, so always verify that the metric conductor meets the ampacity and voltage drop requirements of the specific installation.

Why Wire Diameter Matters

Knowing the outer diameter (OD) of a conductor is essential for several practical reasons. When sizing conduit, the cross-sectional area of each wire (including insulation) determines how many conductors fit — use our conduit fill calculator for NEC-compliant sizing. When specifying cable glands, connectors, or terminal lugs, the conductor OD determines which hardware fits. For international projects requiring metric-to-AWG substitution, verifying that the replacement conductor is close in diameter ensures it fits existing raceways and terminations.

Insulated wire outer diameter (OD) is significantly larger than bare conductor diameter and varies by insulation type — do not use the bare conductor diameters above for conduit fill calculations. The diameters in the table are for bare solid conductor only. The overall outer diameter of an insulated wire depends on the insulation type: THHN/THWN-2 has the thinnest insulation, while RHH/RHW-2 has the thickest. Stranded conductors also have a slightly larger overall diameter than solid conductors of the same gauge because of the air gaps between strands.

Solid vs. Stranded Conductor Diameter

A stranded conductor is made of multiple smaller wires twisted together to equal the same total cross-sectional area as a solid conductor. While the copper area is the same, the overall diameter of stranded wire is larger because the circular strands cannot pack perfectly — small air gaps remain between them. For example, a 12 AWG solid conductor has a diameter of 2.05 mm, but a 12 AWG 7-strand conductor has an overall diameter of approximately 2.32 mm. This difference matters when calculating conduit fill: NEC Chapter 9, Table 5 provides the cross-sectional area including insulation for both solid and stranded conductors, and the stranded values are slightly larger.

kcmil vs. MCM

You will see large conductors labeled in either kcmil or MCM — they mean the same thing. MCM stands for “thousands of circular mils” (M = Roman numeral for 1,000, CM = circular mils). The industry has largely moved to the abbreviation kcmil (kilo-circular mils), which is the preferred term in the current NEC. A 500 kcmil conductor has a cross-sectional area of 500,000 circular mils. To convert kcmil to mm², multiply by 0.5067 (for example, 500 kcmil × 0.5067 = 253.35 mm²).

Frequently Asked Questions

What AWG is 2.5 mm²?

2.5 mm² is closest to 14 AWG (2.08 mm²). The metric 2.5 mm² conductor is approximately 20% larger in cross-sectional area than 14 AWG. In international wiring, 2.5 mm² is the standard size for general-purpose branch circuits, equivalent to the role 14 AWG and 12 AWG play in NEC installations. If substituting for a 14 AWG circuit, 2.5 mm² is a safe replacement since it provides more copper area.

What is the diameter of 12 AWG wire?

A 12 AWG solid bare conductor has a diameter of 0.0808 inches (2.05 mm). With THHN insulation, the overall diameter increases to approximately 0.105 inches (2.67 mm). With thicker insulation types like RHH, the overall diameter is larger. 12 AWG is one of the most common wire sizes used in residential and commercial branch circuits in the United States, typically rated for 20-amp circuits.

How do I convert AWG to mm?

To convert an AWG gauge to millimeters, use the formula: diameter (mm) = 0.127 × 92^{((36 − AWG) / 39)}. For quick reference, use the converter tool at the top of this page. To convert to mm² cross-sectional area, first calculate the diameter in mm and then use the area formula: mm² = π × (diameter/2)². The converter and reference table above do both calculations automatically.

What is the difference between AWG and kcmil?

AWG (American Wire Gauge) is a gauge-based system used for conductors up to 4/0 (0000). For larger conductors, the industry uses kcmil (thousands of circular mils), which directly describes the conductor’s cross-sectional area. The transition point is 4/0 AWG, which equals 211,600 circular mils. The next standard size up is 250 kcmil (250,000 circular mils). Unlike AWG where smaller numbers mean bigger wire, kcmil is a direct measurement — a higher kcmil number always means a larger conductor.

Is 4 mm² the same as 12 AWG?

They are close but not identical. 12 AWG = 3.31 mm² and 4 mm² is approximately 11 AWG equivalent. In practice, a 4 mm² metric conductor is about 21% larger than 12 AWG. For most applications, 4 mm² can substitute for 12 AWG since it provides more copper area, but you should verify that the conductor physically fits the terminals and raceways designed for 12 AWG. Many terminal blocks and connectors are rated by mm² range, so check the manufacturer’s specifications.

What size wire is 1000 MCM?

1000 MCM (also written as 1000 kcmil) is one of the largest commonly stocked standard conductor sizes (1250, 1500, and 2000 kcmil also exist but are less common). It has a bare conductor diameter of 1.000 inch (25.4 mm) and a cross-sectional area of 506.7 mm². The conductor is always stranded at this size (typically 37 or 61 strands) and is used for high-ampacity feeders and services. 1000 kcmil copper is rated for approximately 545 amps at 75°C per NEC Table 310.16. Ramcorp stocks building wire up to 1000 kcmil in both copper and aluminum.

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Disclaimer: This wire size converter and the accompanying reference table are provided for informational and educational purposes only. This tool does not constitute professional electrical, engineering, or code-compliance advice. Values shown are nominal and based on standard AWG formulas and NEC Chapter 9, Table 8. Actual conductor dimensions and resistance values may vary by manufacturer, stranding, temperature rating, and insulation type. AWG-to-metric conversions are approximate because the two systems do not align exactly — always verify that any substitution meets the ampacity, voltage drop, and physical fitment requirements of the specific installation. Building codes, NEC editions, and local amendments change periodically. Always consult a licensed electrician or professional engineer and your local authority having jurisdiction (AHJ) before specifying or installing wire and cable. Ramcorp Wire & Cable makes no warranties, express or implied, regarding the accuracy of this tool and assumes no liability for errors, omissions, or any losses or damages arising from its use.

The information on this page is provided for general reference only and may contain errors or omissions. NEC® is a registered trademark of the National Fire Protection Association (NFPA®). UL® is a registered trademark of Underwriters Laboratories. All other trademarks, product names, and brand names referenced on this page are the property of their respective owners. Ramcorp Wire & Cable is not affiliated with or endorsed by these organizations unless explicitly stated.

AWG to mm Wire Size Converter — Calculator & Reference Table