Wire Gauge Calculator

3 min read 4 steps 7 terms 3 examples 6 FAQs d(mm) = 0.127 × 92^((36 − AWG) ÷ 39)

American Wire Gauge (AWG) is the standard system for specifying wire thickness in North America, and its numbering runs backwards from what most people expect: smaller numbers mean thicker wire.

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Walk-through

How to Use This Calculator

4 steps

Pick a tab

Choose AWG → Size to convert a gauge number to diameter and area, Size → AWG to find the nearest gauge for a measured diameter, or Ampacity to look up typical current ratings by gauge.

Enter a value

Type an AWG number (e.g. 12, or 0 for 1/0) or a diameter in mm or inches. The result updates instantly as you type — there is no button to click.

Read diameter and area

The AWG → Size result shows diameter and cross-sectional area in both mm and inches, so you can match whatever unit your spec sheet or datasheet uses.

Check typical ampacity

Use the Ampacity tab to look up a typical 75°C copper current rating for a gauge, or compare two gauges side by side — treat it as guidance, not a substitute for NEC code.

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Reference

Formula & Methodology

3 formulas

Diameter from AWG

d(mm) = 0.127 × 92^((36 − AWG) ÷ 39)

The American Wire Gauge system is a geometric progression: each step of 6 gauges roughly halves the wire's cross-sectional area. This formula reproduces the standard AWG diameter chart directly from the gauge number.

Cross-sectional area

area(mm²) = π × (d ÷ 2)²

Once you have the diameter, the cross-sectional area follows from the standard circle-area formula. Larger area generally means lower resistance and higher safe current-carrying capacity.

Nearest AWG from diameter

AWG = 36 − 39 × log₉₂(d(mm) ÷ 0.127)

This inverts the diameter formula to solve for AWG, then rounds to the nearest standard integer gauge, since AWG sizes are not continuous.

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Glossary

Key Terms Explained

7 terms

AWG (American Wire Gauge) A standardized numbering system for wire diameters used in North America. Lower numbers mean thicker wire; each 3-gauge step roughly doubles the cross-sectional area.

Wire gauge A general term for a wire's size classification. In the AWG system it is expressed as a single number (like 12 or 1/0) that maps directly to a standard diameter.

Diameter The distance across the bare, uninsulated conductor. This calculator's formula produces the theoretical bare-copper diameter for a given AWG, not the outer diameter of an insulated cable.

Cross-sectional area The area of the wire's circular face, usually given in mm² or circular mils. It's the dimension that most directly determines how much current a conductor can safely carry.

Ampacity The maximum current a conductor can carry continuously without exceeding its temperature rating. Ampacity depends on insulation type, ambient temperature, and how many conductors are bundled together, not on gauge alone.

Circular mil A unit of cross-sectional area equal to the area of a circle with a diameter of one mil (0.001 inch). It's the traditional unit for large-conductor sizing in North American electrical work, alongside kcmil (thousand circular mils).

Gauge (number) The size label itself, historically tied to the number of times a wire was drawn through progressively smaller dies — more draws, a higher gauge number, produced thinner wire, which is why the numbering runs backwards from what feels intuitive.

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Scenarios

Real-World Examples

3 worked examples

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Electrician checking a spec sheet

AWG → mm

Gauge 12 AWG

12 AWG converts to a diameter of about 2.05 mm and a cross-sectional area of 3.31 mm² (0.081 in, 0.0051 in²) — the standard reference figure printed on most AWG wire charts.

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DIYer sizing a subpanel feeder

Cross-sectional area

Gauge 6 AWG

6 AWG, a common gauge for 50-60A subpanel feeders, works out to roughly 4.11 mm diameter and 13.3 mm² of cross-sectional area — more than 4x the area of 12 AWG.

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Measuring an unlabeled conductor

Diameter → AWG

Diameter 8.25 mm

A bare conductor measuring 8.25 mm across is essentially exactly 1/0 AWG, a size commonly used for heavy feeder and welding cable.

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Deep Dive

Understanding AWG Wire Gauge Sizing

4 chapters · 3 min read

American Wire Gauge (AWG) is the standard system for specifying wire thickness in North America, and its numbering runs backwards from what most people expect: smaller numbers mean thicker wire. This calculator applies the exact geometric formula behind the standard AWG chart so you can convert between gauge, diameter, and cross-sectional area in either direction, plus check a typical ampacity guideline for each size.

Why AWG numbers run backwards

AWG sizing traces back to the wire-drawing process: a rod of metal is pulled through a series of progressively smaller dies to reduce its diameter. The gauge number originally referred to how many times the wire had been drawn — more draws produced thinner wire, so a higher gauge number came to mean a smaller diameter. That's why 14 AWG is thinner than 12 AWG, and why the largest common sizes are labeled 1/0 through 4/0 rather than continuing upward.

The math behind the AWG chart

AWG is a true geometric progression: d(mm) = 0.127 × 92^((36 − AWG) ÷ 39). The constants aren't arbitrary — they're chosen so that 36 AWG has a diameter of exactly 0.127 mm (5 mils) and 0000 AWG (4/0) has a diameter almost exactly 10x larger. Because the progression is geometric, every 3-gauge step roughly doubles the cross-sectional area, and every 6-gauge step roughly doubles the diameter — a pattern electricians rely on for quick mental estimates.

From diameter to area, and why area matters

Once you know the diameter, cross-sectional area follows from the standard circle formula, area = π × (d ÷ 2)². Area matters more than diameter alone because it directly relates to a conductor's resistance and current-carrying capacity: doubling the area roughly halves the resistance per unit length for the same material, which is why thicker wire can safely carry more current.

Ampacity is guidance, not code

The typical ampacity figures on the Ampacity tab come from the 75°C copper column of NEC 2020 Table 310.15(B)(16) — a widely-cited reference, but only a starting point. Actual safe ampacity depends on the conductor's insulation type and temperature rating, ambient temperature, conduit fill, and how many current-carrying conductors are bundled together, all of which can lower the allowable current well below the table value. Always verify against the current edition of the National Electrical Code and consult a licensed electrician before sizing wiring for a real circuit.

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Questions

Frequently Asked Questions

6 questions

How do I convert AWG to mm?+

Use the formula d(mm) = 0.127 × 92^((36−AWG)÷39). This calculator applies it automatically — just enter the gauge number on the AWG → Size tab.

What is 12 AWG in mm?+

12 AWG is approximately 2.05 mm in diameter (2.053 mm precisely), with a cross-sectional area of about 3.31 mm².

Does a lower AWG number mean thicker or thinner wire?+

Thicker. AWG numbering runs backwards from intuition — 10 AWG is thicker than 12 AWG, and 4/0 (the largest common size) is thicker than 1 AWG.

What does mm² measure on a wire chart?+

Cross-sectional area — the area of the conductor's circular face. It's a more direct predictor of current-carrying capacity and resistance than diameter alone.

What is ampacity, and is the value here exact?+

Ampacity is the maximum current a wire can safely carry continuously. The figure shown here is a typical 75°C copper guidance value from NEC Table 310.15(B)(16) — actual safe ampacity depends on insulation, temperature, and installation, so always verify against current code.

What is kcmil, and when is it used instead of AWG?+

Kcmil (thousand circular mils) is used for conductors larger than 4/0 AWG, where the AWG numbering system stops. This calculator covers the standard AWG range; very large service conductors are typically specified in kcmil instead.

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