Wire Gauge Calculator

A wire gauge calculator converts an AWG (American Wire Gauge) number into physical and electrical properties: diameter in mm and inches, cross-section in mm², circular mils, resistance, and NEC ampacity. This page does exactly that for every gauge from 0000 to 40, in both directions (AWG to mm/mm² and mm/mm² to AWG), and adds a wire-size advisor that picks the thinnest AWG satisfying both ampacity and a 3% voltage-drop limit.

Use the formula diameter (mm) = 0.127 × 92^((36 − gauge)/39). Example: 12 AWG → 0.127 × 92^(24/39) = 2.053 mm. Enter any AWG (0000–40) in the converter above and it shows diameter in mm and inches, cross-section in mm², circular mils, resistance, and NEC ampacity instantly.

First compute the diameter with d = 0.127 × 92^((36 − gauge)/39), then cross-section = π/4 × d². Example: 12 AWG → d = 2.053 mm → π/4 × 2.053² = 3.31 mm². The table above lists mm² for every gauge 0000–40; 10 AWG = 5.26 mm², 4/0 = 107.2 mm², 40 AWG = 0.0050 mm².

12 AWG is 2.053 mm in diameter (0.0808 in), with a cross-section of 3.31 mm² (6,530 circular mils). Its NEC ampacity is 20 A at 60 °C, 25 A at 75 °C, 30 A at 90 °C, but the small-conductor rule (NEC 240.4(D)) limits overcurrent protection to 20 A.

10 AWG = 5.26 mm² cross-section (diameter 2.588 mm / 0.1019 in, 10,383 circular mils). NEC ampacity: 30 A (60 °C), 35 A (75 °C), 40 A (90 °C); overcurrent protection limited to 30 A by NEC 240.4(D). It is the smallest gauge commonly allowed for 30 A branch circuits.

The nearest AWG to 4.0 mm² is 11 AWG (4.17 mm², diameter 2.304 mm). If your installation requires at least 4 mm² of copper, use 11 AWG or the next thicker size, 10 AWG (5.26 mm²). Type 4 mm² in the reverse converter to see the exact match distance.

At minimum, 10 AWG copper (30 A at 60 °C). For longer runs, voltage drop often forces a thicker wire: the wire-size advisor above combines NEC ampacity with a 3% voltage-drop check. Example: a 30 A, 12 V, 15 m one-way run needs 1/0 AWG because 1 AWG would drop 3.71%, over the 3% limit.

Use 8 AWG copper: NEC Table 310.16 rates it 40 A at 60 °C, 50 A at 75 °C and 55 A at 90 °C, so with standard 75 °C terminations it carries 50 A and a 40 A breaker protects it correctly. One size thinner fails: 10 AWG is only 35 A at 75 °C. 8 AWG = 3.264 mm diameter (8.37 mm², 16,510 circular mils). For aluminum, step up to 6 AWG (40 / 50 / 55 A). For long runs, check voltage drop with the advisor above: drop often forces thicker wire than ampacity alone.

AWG (American Wire Gauge) and SWG (British Standard Wire Gauge) are different systems: the same number means different sizes. 12 AWG = 2.053 mm, while 12 SWG = 2.64 mm. Always confirm which gauge system a datasheet uses; this converter works with AWG only.

Yes: the AWG scale is inverted. 4/0 (0000) is the thickest common size at 11.68 mm, and 40 AWG is a hair-thin 0.0799 mm. The wire gets thinner by a fixed ratio: every 3 gauges, the cross-section halves (and the diameter ratio per gauge is the 39th root of 92, ≈1.1229).

For diameter: gauge ≈ 36 − 39 × log(d/0.127)/log(92), rounded to the nearest integer. For mm², first get diameter via d = √(4×mm²/π), then use the same formula. The reverse converter does this and tells you the nearest AWG plus how far your value is from the exact size.

A circular mil is the area of a circle 0.001 inch in diameter. Circular mils = (diameter in mils)². It is the traditional US unit for wire area: 12 AWG = 6,530 circular mils, 4/0 = 211,600 circular mils. The full table shows circular mils for every gauge.

Low-voltage runs are dominated by voltage drop, not ampacity. Use the wire-size advisor: enter your amps, 12 V (or 24 V), and one-way length. It picks the thinnest AWG that keeps drop ≤ 3% and ampacity ≥ your current, and shows the next two thicker options for comparison.

The numbers come from the same AWG definition (0.127 mm × 92^((36−n)/39)) and NEC ampacity columns, so core values agree. This tool goes further: bidirectional conversion (mm/mm² → AWG), a searchable 0000–40 table with resistance and circular mils, and a wire-size advisor combining ampacity and 3% voltage drop.

The electrical-unit-converter is a broad electrical hub (volts, amps, ohms, Ohm's law, resistor color codes) with a compact AWG ampacity reference. This page is the deep AWG specialist: the full 0000–40 table, mm/mm² reverse conversion, circular mils, per-gauge resistance, and a wire-size advisor. They link to each other instead of duplicating content.

This advisor answers one question: 'which AWG should I buy?', using a fixed 3% drop rule. The voltage-converter has a dedicated voltage-drop tab with DC and 3-phase analysis, 3%/5% verdicts, and max-length calculations. For pure voltage-drop analysis, use that tool; for wire-size selection, use this one.

The table shows NEC Table 310.16 ampacities (copper, 30 °C ambient, ≤3 conductors) as a reference, plus the 240.4(D) small-conductor limits. Real installations must also satisfy derating for ambient temperature, conduit fill, and local code. This tool is an educational reference: final sizing should be confirmed by a licensed electrician and your local electrical code.

No. This converter runs 100% client-side in a single HTML file: the AWG formula, the NEC reference table, and the advisor math all execute in your browser. There are no network requests, no analytics, and nothing you type is sent anywhere.