REFERENCE CHART · CONSTRUCTION

AWG Wire Gauge Chart

Every American Wire Gauge size from hair-thin 40 AWG to service-entrance 4/0 — exact diameter in inches and millimeters, cross-section area, and copper resistance per 1,000 feet — with a live converter above the full printable chart.

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Convert a wire gauge

On the default — 12 AWG — the diameter is 0.08081 in (2.053 mm), the cross-section 3.31 mm² (6,530 circular mils), about 1.588 Ω per 1,000 ft of solid copper. Enter any gauge below.

Result—Enter values above

Enter values to see the result.

How the gauge numbers work

AWG is a logarithmic scale: every 3 gauges, the cross-section roughly doubles; every 10 gauges, it grows about tenfold. The bigger the number, the thinner the wire — 40 AWG is hair-thin, 4/0 is thicker than your thumb. The exact diameter comes from the ASTM formula d = 0.005 × 92^{((36 − n) ÷ 39)} inches, where n is the gauge (4/0 = −3, 3/0 = −2, 2/0 = −1, 1/0 = 0). Every number in the chart is computed from that formula — no rounded lookups.

Reading the columns

Diameter (in / mm) is what you measure with calipers. Area (mm²) and circular mils are what current capacity actually depends on — 1 kcmil (a thousand circular mils) = 0.5067 mm². Ω per 1,000 ft is the voltage-drop column: multiply by your run length to see what the wire itself eats.

Common gauges and what they’re for

Typical uses, not permissions: 18 AWG doorbells, thermostats, low-voltage; 16 extension cords and speaker wire; 14 lighting circuits; 12 receptacle circuits; 10 dryers, AC units, water heaters; 8–6 ranges and subpanels; 4–1 feeders; 1/0–4/0 service entrances. The NEC and your inspector have the final word on every one of these.

The full AWG chart

44 sizes, 40 AWG (hair-thin) to 4/0 (service-entrance). Diameters from the ASTM formula; resistance for solid annealed copper at 20 °C. Print it with Ctrl/Cmd+P — the table prints clean on one reference sheet.

AWG	Diameter (in)	Diameter (mm)	Area (mm²)	Circular mils	Ω per 1,000 ft
4/0	0.46000	11.684	107.2	2.116e+05	0.04901
3/0	0.40964	10.405	85.03	1.678e+05	0.0618
2/0	0.36480	9.266	67.43	1.331e+05	0.07793
1/0	0.32486	8.251	53.48	1.055e+05	0.09827
1	0.28930	7.348	42.41	8.369e+04	0.1239
2	0.25763	6.544	33.63	6.637e+04	0.1563
3	0.22942	5.827	26.67	5.263e+04	0.197
4	0.20431	5.189	21.15	4.174e+04	0.2485
5	0.18194	4.621	16.77	3.31e+04	0.3133
6	0.16202	4.115	13.3	2.625e+04	0.3951
7	0.14429	3.665	10.55	2.082e+04	0.4982
8	0.12849	3.264	8.366	1.651e+04	0.6282
9	0.11442	2.906	6.634	1.309e+04	0.7921
10	0.10190	2.588	5.261	1.038e+04	0.9988
11	0.09074	2.305	4.172	8234	1.26
12	0.08081	2.053	3.309	6530	1.588
13	0.07196	1.828	2.624	5178	2.003
14	0.06408	1.628	2.081	4107	2.525
15	0.05707	1.450	1.65	3257	3.184
16	0.05082	1.291	1.309	2583	4.015
17	0.04526	1.150	1.038	2048	5.063
18	0.04030	1.024	0.823	1624	6.385
19	0.03589	0.912	0.6527	1288	8.051
20	0.03196	0.812	0.5176	1022	10.15
21	0.02846	0.723	0.4105	810.1	12.8
22	0.02535	0.644	0.3255	642.4	16.14
23	0.02257	0.573	0.2582	509.5	20.36
24	0.02010	0.511	0.2047	404	25.67
25	0.01790	0.455	0.1624	320.4	32.37
26	0.01594	0.405	0.1288	254.1	40.81
27	0.01420	0.361	0.1021	201.5	51.47
28	0.01264	0.321	0.08098	159.8	64.9
29	0.01126	0.286	0.06422	126.7	81.83
30	0.01003	0.255	0.05093	100.5	103.2
31	0.00893	0.227	0.04039	79.7	130.1
32	0.00795	0.202	0.03203	63.21	164.1
33	0.00708	0.180	0.0254	50.13	206.9
34	0.00630	0.160	0.02014	39.75	260.9
35	0.00561	0.143	0.01597	31.52	329
36	0.00500	0.127	0.01267	25	414.8
37	0.00445	0.113	0.01005	19.83	523.1
38	0.00397	0.101	0.007967	15.72	659.6
39	0.00353	0.090	0.006318	12.47	831.8
40	0.00314	0.080	0.00501	9.888	1049

Output · formula · meaning

Output	Formula	What it means
Diameter	0.005 × 92^{((36−n)÷39)} in	12 AWG → 0.08081 in (2.053 mm).
Cross-section	π × (mm ÷ 2)²	Current capacity lives here: 3.31 mm² for 12 AWG.
Circular mils	diameter(in)² × 1,000,000	The US wire trade’s area unit: 12 AWG = 6,530.
Resistance	10.371 × 1,000 ÷ circular mils	Solid copper at 20°C: 12 AWG = 1.588 Ω/1,000 ft.

Who uses this

Electricians: checking a gauge against conduit fill and voltage drop on the fly.
DIYers: making sure the wire they bought matches the breaker they’re feeding.
Automotive & RV installers: sizing 12-V runs where every milliohm matters.
Electronics hobbyists: picking hookup wire and checking resistance for a project.

Accuracy & limitations

Diameters are exact per the ASTM B258 definition of AWG; resistance figures are for solid annealed copper at 20°C — stranded wire and heat shift them slightly. Ampacity is deliberately excluded: safe current depends on insulation temperature rating, how many conductors share a conduit, and ambient temperature (NEC Article 310 and your local code govern). If you are sizing a circuit, stop at this chart and open the code book.

Measuring in decimals? The inches-to-fraction chart converts 0.0808 in to a tape-measure fraction, and the fraction-to-decimal chart goes the other way.

Cite this calculatorBright Side Kit. “Wire Gauge Chart: AWG to mm & Resistance” brightoolbox.com, 2026.

Bright Side Kit. "Wire Gauge Chart: AWG to mm & Resistance" https://brightoolbox.com/wire-gauge-chart/ Accessed October 22, 2026.

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Frequently asked questions

What does AWG mean?

American Wire Gauge — the US standard for wire thickness since 1857. It is backwards on purpose: a bigger gauge number means a thinner wire, because the number once counted how many times the wire was drawn through smaller dies.

What is 12 AWG in millimeters?

2.053 mm diameter, 3.31 mm² cross-section — the standard US wire for 20-amp receptacle circuits. Enter any gauge in the converter above for its exact metric size.

Which is thicker, 10 AWG or 12 AWG?

10 AWG — lower number, thicker wire. 10 AWG is 2.588 mm across versus 2.053 mm for 12 AWG, with about 60% more copper.

What gauge wire do I need for a 20-amp circuit?

Typically 12 AWG copper — the standard pairing in US residential wiring. But the breaker, the insulation rating, the run length, and your local code all matter; when any of those are unusual, check NEC Article 310 rather than the rule of thumb.

How is wire resistance calculated?

From copper’s resistivity: 10.371 ohms per circular-mil-foot. Divide by the wire’s circular mils and multiply by the length in feet. 12 AWG (6,530 circular mils) works out to about 1.588 Ω per 1,000 ft.

What is kcmil (MCM)?

A thousand circular mils — the unit for fat conductors where AWG runs out. 4/0 AWG is 211.6 kcmil; 1 kcmil = 0.5067 mm². MCM is the older name for the same unit.

Does stranded vs. solid change the gauge?

No — AWG measures the total copper cross-section, so a stranded 12 AWG and a solid 12 AWG are the same gauge. Stranding changes flexibility and slightly changes resistance, not the size designation.